Reentering cycling again and looking to upgrade my areo levers on my Paramount to STI. The drivetrain is RX100 7 spd. Ive seen some used RX100 STI levers out there on E-Bay but these could have 18 years of wear on them unless they are listed as new. Currently have to kids attending colledge so a whole new drivetrain is out of the question. Will 7,8,9 or 10 105 or Ultegra work? Thank for any input.

Your 7-speed wheels won't take 8,9 or 10-speed cassettes so to use anything with more than 7-speed STI's you would have to change either the hub or at least the freehub body, redish the rim and either cold-set the frame to 130 mm or plan on using a bit of force to make a 130 mm hub fit your 126 mm dropouts.

One possibility, if you can locate some reasonable 9-speed STI's, is the "8 of 9 on 7" technique where you use a 9-speed cassette with one cog removed. This modified cassette fits on a 7-speed freehub but requires 9-speed shifters (with one "click" locked out by the limit screw) and a 9-speed chain.

I share your trepidations about any used STI, particularly very old ones. You might be able to find a NOS set of 7-speed RSX STI's fairly cheap. These were quite good and were current through the late '90's.

https://cgi.ebay.com/Shimano-ST-3303-...QQcmdZViewItem

You can try these but there are very few new units left for sale anywhere.

I'd just buy a new bike with sti rather than put all that money into an old bike. A used bike with say ultegra 9 speed can be had for $500 or less and blow your old bike out of the water. A mail order bike new with 105 10 speed can be had for under $800.

One of the first things to go on a used pair of sti shifters is a little nut inside that holds the shifter body onto the lever. I've brought many of these back to life by just tightening that nut up with some locktite.
So a good used pair of sti shifters may be worth the risk.

Loosescrews has Sora 7-speed/double STI.

https://www.loosescrews.com/index.cgi...d=290052515207

Personally I would not buy used STI levers unless I was able to inspect them and make sure they actually work. But even if they work fine, you really still won't know how worn the internals are and how much life is left in them. My old STI levers worked fine (for about 5 years) up until the day they didn't

"8 of 9 on 7" will work only if your hub is HyperGlide freehub. Early 7-speeds were freewheel or Uniglide freehub. HyperGlide didn't come around until about '89 or maybe '90 for RX100.

depends on how many of those 7 speeds you hope to use with a shifter with 8, 9 or 10 speeds..lol they can work but will feel like square pegs for round holes.