You are forgetting that USB imposes limits on the number of keystrokes that you can hit at the same time.

There are a few other downsides that may or may not impact your play, depending on how you play.

"Be careful about choosing a USB-based keyboard to hack. The USB keyboard interface is designed to limit the number of simultaneous possible keystrokes to six. This isn't a problem when used for games such as Pac-Man or Donkey Kong, which are unlikely to need more than two or three keystrokes at the same time. However, modern games such as fighting games can easily require many more than six simultaneous keystrokes, particularly if you are building a four-player control panel. PS/2 keyboard encoders often have a maximum simultaneous keypress limit as well, but it's typically between 10 to 20 or so, and unlikely to cause you issues unless you are building a four-player panel. "

I don't know about you, but some of my macros are 2 or 3 keypresses each (alt, ctrl, shift are excluded). In reality, you can work around it but I went PS/2 and avoided it. In really intense PvP, it could be a serious problem because I am healing and doing DPS at the same time as trying to mash WOTF or something else. Plus, you can't really multicast USB in hardware, unless you use Keyclone which did not exist 3+ years ago.

So, in the end, both are *viable*, just be aware of the inherant differences of USB.