in my experience with potted cacti i think a smaller pot is better than a larger one. Just keep them snug but not overly root bound. larger pots lead to poor drainage and i find the tighter the roots are the faster things dry out. cacti drink water fast because in nature they are used to just getting short bursts of water here and there, therefore you shouldnt allow your soil to stay wet for long at all. ive seen 6 foot cacti in 6" pots before, thats a bit overkill but as you can see pot size really doesnt matter.

just my two cents. 8)