straight 1080 blu-ray rips run at about 5 MB/s.
so 720 files should be no problem.
also what are the files streaming from? if they're on a USB drive to begin with, then you're already limited by USB speeds at that end.
a quick and dirty way to see if a file will play.
in finder copy that file to your desktop (you don't have to let it complete, so don't worry about available space), once it get's going if the finder estimate of time to copy is less than the running time of the video, then you'll be ok. you can then cancel the copy.
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also please note
mb and mB are 2 different things. (same for gb and gB)
mb = megabit
mB = megabyte
8 mb = 1 mB
USB 2 = about 240 Mb/s or 30 MB/s (real world speed)
ethernet = 10/100/1000 Mb/s or 1 / 12 / 125 MB/s