It depends. On theory, when making fp32 calculation, CELL is a beast.
IF ( big IF) one is capable to write a program using efficiently all 7 SPEs - that includes algorythm & writing on assembler...
If you need fp64 (IEEE compatible floating point), then Opterons will win IMHO in real-world cases...
HellRipper, this is Beyond3D, not a random forum for people to ask already discussed questions on. There have been billion of debates (with better introduction posts to boot) on this subject, and it's called the search function. Furthermore, please do try to post in the appropriate forum subsection in the future.