Wondering if the P4's Hyper Threading, 800mhz FSB ( its 533 on my Cel-D) 2mb L2 cache ( 256kbit on the celeron) So will the major increase in cache size and FSB boost and HT mean a Noticable increase in a computer used for media applications. Anyone have any benchies?
Well if the media is video, then a higher memory bandwidth is certainly going to provide a noticeable performance increase!
Also 256KB (not Kbit btw) isn't going to hold up against 2048Kb.
Both those reasons are why the Celeron was a cheaper processor, and if I remember correctly, they were just P4's with bad cache. I've got the same P4 chip at home just sitting there, I wont get enough money to make selling it worthwhile, so I imagine your decision (with regards to cost) should be very simple.
I don't have any benchmarks for the Cel 2.8 but I can say the Core 2 Duo E8500 @ 3.16Ghz is approximately 4x as quick as the P4 3.0 CPU (I used the same hardware and swapped chips). So if you're wondering about getting something a little newer without going crazy, the Core2 chips are a massive step up (and the new motherboards backward support the older P4 chips too, which makes upgrading to Core2 a wee bit easier).
Someone who is asking about upgrading to a P4 chip, is not going to have the money for an i5/i7 setup. That's why I suggested the 775 socket chips. When you're on a tight budget, futureproofing goes out the window.
If he bought new motherboard and RAM (and video card if needed), he could make use of it before getting the new CPU as both of the chips mentioned will work in P35 or P45 boards.
(On a side note I don't think there is a huge future in 775, its not EOL but I'd say it's end-of-development, it bores Intel now. My next upgrade will be X58 for the reasons in the post above, the 1156 socket will drop off I reckon).