Bandwidth and timings are two completely different things, I'm not saying one is more important than the other because you can't have bandwidth without timings right...
The reason the bandwidth would be different between 2-2-2-6 and 2.5-3-3-6 is the two middle numbers (ras to cas and ras precharge I believe) THOSE effect bandwidth more than anything, whereas the cas latency and the cycle time (end number) effect primarily stability and not so much bandwidth.
In regards to 1 or 2 FPS gain that could be all kinds of things.....that isn't necessarily the RAM there....if you run a benchmark you're never going to get the exact same numbers both times because computers just don't work that way...theres always that "margin of error" in which that 2FPS could easily fall into.
It takes a good leap in the memory MHz with a decent amount of bandwidth gain before you'd see a substantial increase in FPS really in a real gaming environment.....if you run aquamark, 3dmark01, and programs like that you'll see the difference more than you would while playing your favorite game, primarily because it's not like theres a set FPS that your game will always run at, so the benches will always be inconsistant.
In overall computer speed the RAM with the same timings but higher frequency would obviously perform better.