Depends which encoding software you use between A64 and P4HT..definity don't get Athlon MP..dated and slow.
Because of price I'd recommend a A642800 with chaintech VNF3-250 for $200 combo.
Between 2.8C and A642800
AMD wins
Codecs: xVID
Consumer programs: Ulead VideoStudio 4,5,6 and 7. Roxio videowave 4,5,6 and 7. Pinnacle studio 7 and older.
Mid range video edition: Adobe Premiere 6.5 and older. Ulead MediaStudio Pro 5, 6, 6.5 and 7
MPEG2 Encoders: Canopus procoder, Ligos, bbMPEG.
DVD transcoding: DVD2AVI, VirtualDubMod
Freeware: VirtualDub.
Streaming: Quicktime.
Intel wins
Codecs: DivX 5.1.1
Consumer programs: Pinnacle Studio 9 and 8.
Mid range video edition: Adobe Premiere 7 and newer
MPEG2 encoders: TMPGEnc, mainconcept
DVD transcoding: XMPEG, FlaskMPEG
Streaming: Windows media 9.
Edit: you should always buy the lowest regaurdless of budget and turn a tortise into a hare by overclocking
Edit2: another consideration is memory. You can get away with one stick with the A64 without loosing any performance. If you buy the p4 you must use two sticks or else suffer big time. Using two sticks will cost a bit more at same MB.