FYI
I have a 200GB external with all my MAME junk on it...the PC it's running off is an AMD 733MHz...USB1...I haven't really had any problems, though games like Simpson's Bowl, Killer Instinct, Virtua Fighter, Hard Drivin, etc won't run properly...I assume this is a PC problem and not a speed fromthe external problem...
With some games I do notice a little longer load times...this is due to the external drive, because if I run the same game from c: it loads quickly...