My ship builds for
Ring Runner: Flight of the Sages almost all assume you have an NKRO keyboard, and the hand techniques needed to make use of it...but that's as much about that game's lack of weapon groups as it is about a keyboard's general suitability for gaming.
On the speed front: MX 6.0 is fast, Logitech is faster (most likely the same tech that gets them to the front of the charts in mouse button lag comparisons), optical (and probably Hall effect as well) is fastest. There are a couple of cheaper Asian boards that I suspect might come out around the same as Logitech as well. Topre isn't as fast as you'd expect given that it's a non-contact switch. The top-runners are within about 1ms of each other, with Topre and its clones about 4ms behind, and everything else (with 1000hz polling) another 15-20ms back. I'd think, though, that these differences, even in the bigger cases, are probably more important for performance enthusiasts than they are for gamers. Though, subjectively, I do feel just a bit more competent pulling off fancy in-game movements with my Hall effect board than on anything else...
Now, as for features, the one you see marketed to gamers all the time is the presence of dedicated macro keys. Whether this makes a difference or not will depend on whether you're actually playing something where there are either a) commands where speed matters that you want to move closer to your hand's normal position without having to move any other command away, b) multi-action command sequences that you can condense to a single macro key press to increase your speed and consistency, or c) both. Higher-end non-gaming boards may feature some sort of programmability, but standalone macro keys can be used without having to bind over one of your regular keys or resort to a combination. I actually think it's rather a shame that we don't see this feature more often, since it also has non-gaming applications (especially if the keyboard and its software allow you more freedom than just having a macro key send a preset sequence).
I'm looking forward to seeing what Wooting can do with their analogue switches. Personally, I hate the feel of game controllers-- waaaaaaay too much reliance on thumb dexterity for me-- so if analogue sensing can give me a good substitute for playing games that are usually best-suited to controllers, I'd be all over that.