I run B4 & T4 on the track I also happen to own, and currently have one Maxamps 6000 and one Protek 4000. I'll be buying more Protek, especially if they come out with higher mAh packs. Pack works well, and thus far survives the 2C charging as advertised. It's very light and thin... kind of a pain to swap to the thick MA pack for a longer main.
I use about 3250mAh off the Protek in the B4 for a 15 minute main. Truck (which draws more power) won't quite make 15 minutes.