My $.02 on runtime: I have a converted 8ight-T with a 1515/1y and a Quark 125b. I use either 13/48 or 14/48 gearing depending on track length and difficulty/elevation change. The longest I have ever run on the 3700 packs I have is 10 minutes and 8 second before hitting the 3.0v cuttoff on the quark. That run was with the 14/48, the top end dialed back about 10% and semi-conservative throttle control. Recharging, the batteries accepted almost 3900mah. I would think that runtime, even with an 8000, would be somewhere under 25 minutes at race pace with that settup. Also, like other people stated, the Quark definitely requires a heatsink and does'nt like high air temps and humidity. 15 or 20 minutes in temps over 90 degrees really gets one hot!