Well, I run a few games from an external myself. All of them are low requirement games like visual novels, the sims (original) and a couple doujin games (suzumiya haruhi no gekidou is teh lols) but I see no drop in performance for them. I suppose if you are playing a faster game you would see a difference due to the necessity of the data transfer vs it being directly on the computer itself. I just transferred all my media (pics, doujins, music, videos, etc) to my external freeing up tons of space on my computer itself for my more system heavy games.