Here is a comparison of Seek Times between the two drives <A HREF="http://www.seagate.com/cda/products/discsales/desktop/" target="_new">7200 ATA-66/5400 ATA-100</A>. This is just my opinion the the 7200 rpm (8.2 seek) would be faster, but the 5400 rpm (8.9 seek) would be quieter, practically thinking.
I compared the 20 GB HDD's 7200/66-vs-54/100 as reference.
Fisher of men
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.