Bankrolls and 6 max tables

[arizona]

Hi, I've been playing 3 tables of 3-6 and my bankroll is currently 300 big bets. Lately I've suspected that it wouldn't hurt to increase my bankroll. What do you guys think? Is 300 BB enough or should it be higher? What if I play at higher limits (5-10, 15-30, etc)? Do I need a larger number of big bets or can I get by with the same amount (even if that amount happens to be over 300) regardless of the limit played?
Also, what are the $5-10, 6 max tables like at Party? Are they easy to beat? I've never played at a 6 max table before. Do I need to play differently? In what way? Why are there so many 6 max tables at 5-10, but not at 3-6 or 15-30? Any responses would be appreciated. Thank you.