On the issue of Multi-Tabling...

Since I've been getting better with ABC poker recently on 25NL, I've been trying to keep as many as 10 tables going at once with PA Hud. I cannot notice a difference in my play. To me, I'm playing exactly as I would with 4 tables going. The thing is, I've been noticing a difference in my bankroll. My sessions have either lost me a little bit of money or I've broken even (sessions usually last me around 2-3 hours). It's very frustrating and I don't know if it's because of variance or the bad play I've been making sub-consciously with so many tables going on at once. If I've played over 40,000 hands and feel moderatly confortable with ABC play, how many tables should I be playing at once to maximize my BB/100 ? Thanks for the responses.