Kool Stop make Dura and Dura 2 pads, which both fit the same Dura Ace-style holders:

Kool Stop Dura
Kool Stop Dura 2

Apparently, the Dura 2 is (per Kool Stop) "newly designed"; Harris Cyclery call it an "upgrade" from the Dura, but the real difference - same compounds - is that the Dura 2 is thicker and has no "plow tip".

Ceteris paribus, thicker = longer life = better, but is the plow tip a gimmick, or a feature worth having? For the sake of argument, this is on a bike that would very, very rarely see mud.

The plough tip is more about skimming water off rims than mud IIRC. I use Dura 2 and they're fine, so I guess I don't know what I'm missing.

I have heard of folks filing down the "plow tip" in a effort to stop squealing/chatter, perhaps this is the "upgrade" to which they are referring. The plow tip appears to stand somewhat proud of the rest of the pad when new, I can't see that the tip will accomplish much after it has gotten worn down flush with the rest of the pad.

The Dura-2 brake pads are narrower, and so are a better choice for rims with a narrow brake track. (I used "brake track" to refer to the area on the rim available for the brake pad to contact, not sure I'm using the right terminology) . I used the original Dura pads with Velocity Synergy rims, which have a generous brake track, they worked nicely. Now I'm using Velocity A23 rims, which have a pretty narrow brake track, so I'm using the Dura-2 brake pads with very good results. Overall braking performance seemed the same with either version.

Do any of them not howl like a stuck pig?

On the cheap Canti's I had them on, every stop in a group ride was embarrassing no matter the tow in setting.

the plow tipo is a toe-in aid, and wears off fairly quickly, though it can cause some added squeal when new. You can do without and use a dime or piece of cardboard as a toe-in guide instead.

They need to wear in, not just the pads but the rims as well!

Mine were fine until recently, when I replaced the wheels on my cross bike with some Archetypes, and the breaks now howl no matter how much I toe them in. I expect after a few hundred miles they'll quiet up again, maybe after all the anodizing has worn off the Archetype rims!

Surely the dime will fall off when you brake?

Sorry.

Thanks for the comments everyone. I have a set of Dura 2 in hand, having previously used Dura and was trying to decide whether it was worth the hassle of swapping them. Seems the consensus is that the plow tip is no great benefit.

Very interesting information. i have 7 pairs of new Kool Stop Salmon inserts in my parts box waiting for the current ones on my bikes to wear out. I bought them in two groups when web store orders needed a couple of extra items to get above the free shipping threshold. I just looked and 4 are Dura and 3 are Dura 2. I never noticed they weren't identical until I read this thread. The rims they will go on have plenty of brake track width so I expect which I use won't matter.

Once you have Ultegra 6800 brakes, why would you want for anything else?