Shader Clock = Memory Clock
If you don't know, don't say...
ATi does not allow to change shader clocks, as there so many of those and they cannot quarantee that all of them works when overclocked.. NVidia doesn't have so much shaders, but they're much more faster than ATi's..
HD 5770 good sides:
DX11 support
Average of three FPS more in games, such as Call of Duty: WOrld at War
Does not get so hot as GTS 250
GTS 250 good sides:
It's nVidia, as most of the games are "modified" for nVidia.. (The way it's meant to be played), meaning it'll get higher FPS in those games.. (Crysis, CoD2, 4, 6, Far Cry 2, San Andreas etc..)
GTS 250 bad sides:
No DX 10.1 support.