[Fielding lol]

Most winning players will lower their PTBB/100 while multitabling, however, they are getting in many more hands and make more money in a short period of time because of this.

You need to analyze the difference in your PTBB/100 when multitabling and when you're not. The amount you increase your bankroll for multitabling should be directly related to how much your win rate is lowered due to multitabling.

Something else worth mentioning, if multitabling is causing a significant drop in your win rate make sure that you are easing in to it and working up tables as you feel comfortable with them.