I'd google that, but I'd venture to guess and I think I read it around here somewhere else that the iMac would probably handle things a bit better, but the video card in the iMac is still inferior...I think.
Decoded that's 1828 for a late 2005 Dual CORE 2GHz G5 or 1688 for a June 2004 Dual Processor 2GHz G5 vs 3740 for the iMac 2.8 GHz. More than twice as fast.
Well that would depend on how many cores you use for each program you want to run. I'd like to see a comparison of Toast 8 DVD image encode on the Quad G5 which uses all 4 cores vs. the iMac Dual 2.8 which can only use two.