A PC hard disk (3.5") will spin at 7,200 r.p.m. which is faster than a laptop (2.5") at 5,400 and that's about as good as it gets in USB2.0. USB 3.0 might transfer faster but I doubt you'd notice the difference. SCSI disks spin at 15,000 but cannot (as far as I know) be converted to fit a USB caddy.
USB 2.0 drives transfer around 40Mbps. This is actually faster then what a DVD can do. (you can use an IDE ATA/33 cable) You should be able to use a normal USB 2.0 drive for what you want to do. If you have already tried this and it failed, what are your system specs? Perhaps you have a weak link somewhere else.