Just upgraded an ebay sourced Emaxx 3906 that I've had plenty of fun with over the past 2 years to brushless and A123. Running two 6S1P packs in parallel for 19.8 volts. The difference between stock motors with two 7-cell NiMH packs is incredible. Previous maximum speed is achieved at about 60% throttle. Many thanks to the many postings on this forum that guided me to selection of ESC, motor and gearing.