Pentium 4 optimisation?

I'm asking this here, because I do most of my transcoding (MPEG-1 to DivX 5.02) with VirtualDub. Are any of the main utilities used by doom9.net regulars optimised for SSE2 on the Pentium 4? I need a new computer, and am trying to decide whether to go down the cheaper Athlon XP route, or to shell out for a P4.

DivX5 is optimized for P4. Avisynth (mpeg2dec.dll) is optimized for P4. VirtualDub isn't as far as I know. With 2 out of 3 optimized for P4 you will hardly see any speed loss compared to 3 out of 3. Just buy whatever CPU you want and can afford, either way it's not going to make much difference in encoding speed anyway.

@Acaila: This may be a silly question, but what does make a difference in encoding speed? Edit: - My apologies, I just found another thread, with answers.