need help with cpu

[pwillats]

hi all, i need your expert guidance, first of all i will give you my ageing setup details, msi p35 neo2 mobo, e6750 core duo, 2x 3780,s in crossfire,550w antec psu and 4 gig of xms2 ram running on windows7 64...anyway here goes, im a wow and cod player and would like to update my system, i have a £350-400 budget and am looking out for a quad,new psu and a gtx 460,
Q1. is either a q8400 or a q9400 compatible for my mobo, if so is it a easy installation process?
Q2. do i need an upgrade on my psu for a gtx460
Q3. am i looking at right things for a performance boost for my rig for gaming guys

with regards to question 1, will i need to flash the bios (something i have never done b4) for a new cpu

look forward to reading your answers, cheers guys in advance

 

[pwillats]

thnx for that zero, i would get a 470 but that would put me over budget, unless my existing psu can handle it, what about the bios flash before i put the new cpu in? someone said this has to be done, is this right? not sure myself cuz ive never changed cpu,s before just built from scratch

 

[pwillats]

its just a thought, if i decided against a quad and just stuck with my 6750, would there be a serious bottleneck with a gtx 460/470 guys??

 

[pwillats]

aah ok zero, thnx again, all i need is for someone to give me a step by step guide to overclocking my good old 6750 then, and also recomend a decent cpu fan before i do so, i have tried overclocking it b4 but got many bsod,s so i gav up, maybe i was doing it wrong