servo may show specs at 7.4v, but they still work at 6v and lower in a 12th car. just have different performance stats but function on a 1S pack, and a 1S esc, or 2S esc with booster or rec pack. list of servos at front of this thread some all work fine

dumping and power robbing you experienced with inefficient brushed motors and limited power Nicads or even Nimh cells is pretty much gone

racer at track has this, no issues http://sanwa-denshi.com/rc/car/servo/srg-hr.html, the SRG-HS says 3.7 v

i run a 7000mah lipo, doing 4-5+ warm up laps, (never did that with nicads) and 8 minute run, when i recharge pack it takes around 2300mah. i even ran my 7000 pack once two 8 min runs with 17.5T motor no problems