I have a 6600GT in my desktop system (3200+Athlon64/1gb DDR) and I have a 6800go in my Inspiron 9300 (PentiumM740 1.7ghz/ 1gb DDR2)
My 6800go scores:
3885 in 3DMark05
8732 in 3DMark03
My 6600GT scores:
3440 in 3DMark05
8235 in 3DMark03
Even with a more powerful Athlon64 cpu...my laptop's 6800go still outscores my 6600GT in every "graphics" benchmark (but definitely doesnt kill it).
Of course, my PentiumM gets spanked by the Athlon64 in all CPU benchmarks.
Still, I do all my gaming on my laptop because the slower CPU has never been an issue when gaming so far. The PentiumM is strong enough.