you may want to verify that whatever programs he is using will actually work better on a p4 system. 1 1/2 yrs ago the p4s pwned amd @ encoding, but in that time amd has made up a lot of ground and now the amds are just as good at encoding(software dependent) as a p4.
also, about hitting 4GHz+ on air, i would like to know what the people's ambient room temps are because that has at least some to do with it.
other than that i would recommend:
ram - OCZ
psu - enermax, seasonic, antec or pc&p
hsf - xp90 flavor of hs that fits your cpu along with a 90mm fan
m/b - any of the big manf, like asus, abit, intel, dfi, gigabyte, epox
sorry if this is too general but that is where i would start. the reason i ask about the software is at least in the past certain software was optimized for p4s vs the competition, not really sure if this is a issue any more.
and i am not pro amd (look at rig in sig) but i am pro whatever gives me the best performance for my most important / cpu intensive application for the $$$.
also consider that if you are going to o/c a p4, compare to how it fairs compared to an o/ced amd cpu of equal costs. GHz are not everything as different certain cpus do more instructions per cycle than others