I have always used bulk cables for my XT shifters (about $2, "prestretched" stainless cable) but recently got a sales pitch for coated brand-name shifter cables (about $12) which, I was told, will not stretch and will work better.

I have never been aware of a problem with generic cables. Am I missing something?

Not really. I've used everything from no-name bulk cables to fancy Jagwire with the black teflon coating. Never really noticed a difference.

Now housing, that's where the differences become apparent.

I prefer Teflon coated cables which are a bit more expensive then bulk stainless. I use them mostly because they don't corrode as much as stainless during winter riding. Stainless is more susceptible corrosion from salt infiltration. But, for general riding, bulk stainless works just fine.

As for the cable not "stretching", that's probably just marketing. All of the cables are cut off a spool of pre-stretched cable but the action of cutting the cable releases a bit of tension on the cables and allows them to unwind a little. That's all cables. I have yet to run across a cable that doesn't need a bit of time to bed into place and thus need adjustment. I suspect the expensive fancy ones will need do the same. It's physics.

I prefer die-drawn un-coated stainless cables in PTFE-lined housings. There is little if any difference in frictional coefficient between PTFE on steel and PTFE on PTFE, and I have found that the coated cables are difficult to clamp effectively and are prone to the coating peeling.
My understanding is that "stretching" is more of the cables bedding in to the housings than of the metal actually elongating. This even occurs when just replacing the inners; they have to wear their own groove into the housing.

I've used slick galvanized cables for decades with no issues. I like them because I prefer to solder the cut ends. I don't ride in snowy weather, though, so I can't really say if winter e=weather would change my mind.

FWIW, I doubt that cable stretch actually exists. May belief is that the cable housing ends bottom in the cable stops which makes the housings a little bit shorter.

Glad I resisted the sales pitch. I'll stick with the $2 version.

Having worked with cables I can tell you they do stretch in two ways, 1) the more significant settling of the wires in the strand and in cycling the insignificant stretching under loading of the metal itself, Hookes Law.

As I stated above, the main reason for using Teflon coated cables is to avoid corrosion of the cable when exposed to salt. Stainless isn't resistant to salt corrosion. I've pulled many cables out of housing that is lined but the cabling was coated in salt induced corrosion products.

I disagree. First, cables need adjustment after initial installation. That is a given. New inner cables always require some adjustment of cable tension. Others have suggested that the cable tension adjustment is due to the outer cable settling into the ferrules but cable tension adjustments are always needed even if you are using old housing. The simplest explanation for new cables needing tension readjustment is elongation of the wire cable as the cable strands twist slightly tighter when put under tension.

Cables of all varieties do stretch, from bridge cables to crane cables to bicycle cables. There is even a formula for calculation how much a cable will stretch under loads based on the load and the diameter of the cable.

Well, we have to separate elongation under load (elastic deformation) from a permanent slight elongation when a new cable is first put into service as the strands bed-in against each other and/or settle into the end ferrules. The first type occurs with every shift and is automatically compensated for while the second type occurs initially and is why minor adjustments to the cable "tension" are needed for the first ride or two after a new cable is installed.

I try to compensate for the bed-in type of elongation by pulling firmly on the cables before making my initial shifting adjustments. I usually works so only very minor adjustments are needed after the first ride.

BTW, if you do use teflon coated cables, be certain to scrape the coating completely off where the cable clamps to the derailleur. Otherwise the cable WILL slip no matter how much you tighten the clamp bolt.

There are formulas for both elastic deformation and permanent elongation. But, yes, I'm talking mostly about the second type. Settling into the ferrules is much less of a problem than many people make it out to be. I use metal cable housing ferrules so there is no "settling" in of the cable housing into the ferrule and I seldom see any difference when using new outer cable. But I do see "stretch" of the inner cable due to the bedding of the cable. This is the "stretch" that many people deny exists.

I agree that this helps but it doesn't solve the problem entirely. And, again, it's the bedding in that I'm talking about and that many people deny exists.​​​​​​​

I've never had a problem with the cable anchoring properly. The teflon coating is very thin and teflon, while slick, is also soft and deforms easily under pressure. I don't use noticeably more pressure on the anchor cable and my Teflon coated cables aren't overly deformed at the pinch bolt over uncoated cables.

Die drawing the cable after it is made up slicks the outer surface of the cable, by flattening the metal.

helps reduce the friction the return spring , at the back end , has to work against..

As you may have guessed, I have. The first time I used teflon coated cables I just tightened the clamp bolt the same as always and on my second ride the shifting wen't all wonky. Not, slightly like from minor bedding but really bad, like two cogs out of phase. When I got home I found the cable had slipped through the clamp about 5 mm. So, I realigned it and tightened the bolt a bit tighter. Two more rides, same problem. This time I carefully scrapped the coating off for about an inch each side of the clamp area, tightened the bolt normally and no more problems. YMMV

It's something to watch out for.

What's the effect of non-elastic cable stretch? You have to turn a barrel adjuster occasionally.

What else causes the barrel adjuster to need turning? Wear in the shifter and derailleur, wear in the housing, etc. So eliminating stretch slightly reduces the need to occasionally turn a barrel adjuster. It's your money.

I use Jagwire Teflon coated cables on every bike I have and the bikes I've built for my daughters. Never a slipped cable.

Barrel adjustments are a rare occurrence for me. YMMV

Good, drawn stainless steel cables work very well but I do like some of the higher end cable options; they do feel just a bit slicker. The newer Shimano optislick works well and doesn't shed like their earlier PTFE cables.I have some Bontrager branded coated cables on my road bike that feel great. Maybe my favorite is the polish ground Jagwire pro cables. No coating, just really really polished exterior.