Let's try to clear up a few things here and hopefully help some of you folks out. I recently did an upgrade from a Mobile @ 2.6Ghz to an
[email protected] and then a A64 3400 (socket 754) which is running lightly OC'd at 2.5Ghz. All the rigs were tested with Corsair XMS ram running 5-2-2-2 T1 and a 6800Gt @ Ultra clocks, harddrive used was a 74gig SATA Raptor. This setup includes the Mobile as I bought those parts during upgrades over the last year.
Anyway the p4 build was done mostly out of curiousity and came about due to a couple of coincidental things coming together. Lets clear this one up right now. Forget stock P4's if you do any gaming at all, overclocked above 4Ghz they are good, stock the 3.4Ghz was hammered by my Mobile rig in back to back tests done by yours truely, I will brook no argument about it.
After the P4 was broken up and sold off I decided to spend some cash on an A64 rig and after doing a lot of reading decided the 939 was not worth the extra cash over a 754 for the minimal boost it gives. As PR ratings have grown the gap between highend 939 and 754 is widening slowly but it's still not as great as you would think with all of the benchmark junkies ranting and raving that goes on around here. Honestly I doubt anyone could sit at a 939 and 754 side by side and tell any difference at the same clock speeds.
Not to wander to far off topic, comparisons between my Mobile @ 2.6 and my overclocked A64 3400. You will notice a bit smoother game play at higher resolutions due to the memory bandwith and cache latency advantages the A64 enjoy's over XP systems. Dont misunderstand me though, the difference it not that great. In some games you will be able to play at a higher resolution but the differences are not extreme and if your not a hardcore gamer (someone who currently has HL2, DOOM3, NFSU2, Rome TW, WOW, and BFME sitting on thier desk is hardcore....someone with only 1 or 2 titles is not) your money would be better spent on a high end video card than building a new rig built around a slower A64.
Lastly I generaly follow a simple rule around upgrades, when the PR rating doubles it's time to move on. Since the PR rating of a Mobile at 2.6 falls somewhere around 3800-4000 I would say you will see only minor noticable improvements in speed if any by moving to a low end A64 rig. I made the move because I had money in hand and was curious, given the choice today I would have waited for NF4 and SLi boards before upgrading from the Mobile @ 2.6.