it'll depend entirely on the specific drives. 7200 rpm will have a faster seek time for sure, but if you're copying big contiguous files, you need squential read speed, and there are some decent 5400rpm drives out there now.
I don't think either will sustain even 66 MB/sec - seagate's new cheetah 15000rpm drive pushes out about 50MB/sec over scsi... (www.linuxhardware.org)
probably the 7200 rpm drive will be faster overall, as it can get to the files (or fragments) faster, but for pre-cached files, the 5400/100 will be able to burst them faster.
I just compared a couple of drives on Seagates site, and an older 7200/66 had an avg transfer rate of 30MB/sec, while a newer 5400/100 scored 14.5MB/sec.
I'd go for the 7200rpm.