your winrate typically drops as you add more tables exposing you to more variance.

No no no! More tables = LESS variance, or rather more hands = less variance. Your win rate CAN drop because of a number of factors:

- You go on tilt and it affects all the tables on which you're playing (ditto tiredness, boredom, inebriation)
- you can't take as full an advantage of reads
- you get hurried/flustered/overwhelmed when all your tables require attention at once

However, it can also help - you get less bored, you slip into a groove more easily and don't get distracted, and of course good play on one can encourage you on others.

So, theoretically, you don't need a bigger bankroll, but you can theoretically take a bigger hit the more tables you play so psychologically you might want to make sure that ypur roll is big enough for any loss to leave you down but not out.