A 4000+ desktop processor is 2.6 GHz 62 watts
The MT-40 is 2.2 Ghz 25 watts
Both have a 1 MB Cache
Another thing you didn't ask about, but is worth mentioning is that the new ML-44
is a 2.4 Ghz 1 MB cache chip that uses 35 watts of power, possibly a closer match, but is very
pricey and hard to find.
The ML-42 is 2.4 GHz with 512 kb cache (but performance wise very
close to the ML-44 because the cache on a Turion or Athlon does not have a humoungus impact on performance, due to the onboard memory controller). The ML-42 is a cost effective way to add the clock cycles back to your gaming beast and still not hold a gun to the head of your battery.
I think your cost in battery performance is not worth the couple clocks you're picking up with the more power hungry Athlon Mobile over either of the Turion family ML or MT. I mean, it is a notebook, it probably has a big role in your life aside from gaming, namely mobility, and to work on the go you don't always have power available.http://www.killernotebooks.com/images/logos/insignia_small.jpg