I would say so......
do the math tho..... I have Austin Powers 2, approx 91 minutes in a good quality 700MB DivX 5 rip (which I did myself BTW)
91 * 60 = 5460 seconds
700 * 1024 = 716800 Kilobytes
716800 / 5460 = 131.28 Kilobytes per second is required to keep this movie playing.
as a rule of thumb I guess if you can achive 150-200K per second you should be in the comfort zone with that one. I have no idea on the max throughput of USB IDE adaptors - little help?