Civickiller80 has it just about right, in my opinion.
Tits can never be too big, skirts can never be too short. However, I have my own limits. Since I don't know cup sizes that well (I don't wear a bra because I'm a dude), I'll reference some well-known babes that get me off on a semi-regular basis.
Minimum: Aria Giovanni or Erica Campbell
Maximum: Chelsea Charms or Crystal Storm
Dixie Dynamite was too huge. I also don't like them when they're big, but they flop like deflated weather balloons.