its kinda rare to overclock RAM without overclocking the CPU.
Higher latencies will mean a slower machine, but I doubt anybody will be able to tell the difference. Any difference will only show up on benchmarks, and it will be quite slight.
You'd do better going with as loose timings as you can possibly get, and increase the speed instead. 1066, 1200, whatever you can get, as long as its stable. Run Prime95 or memtest as long as possible just to be sure (at least overnight, I'd be happy with 24 hours).