[aces961]

This really depends on how you define your win rate and varience. If you do so in terms of Big Blinds per 100 hands, then when you play 4 tables if your win rate stays the same then your varience will stay the same. Now if you define it as big blinds per hr then assuming 4 tables corresponded to a increase by a factor of 4 in win rate, your standard deviation would go up by a factor of two.

The risk of losing your bankroll after a certain number of hands would be the same in either of these cases assuming your win rate per 100 hands per table stayed the same no matter how many tables you play.

Now in reality there will probably be a decrease in win rate per hand as you go to more tables so your risk of going broke in x hands will be higher if it was done at multiple tables than at one table.