I have talked with Castle and have also received the 280k number. My wife is running a 870kv 14-pole outrunner on 6s with a MMP 1-cell ESC in her TLR 22T Stadium Truck. So, her numbers are 25.2 volts * 870 = 21924 RPM * 7 = 153468. We have had zero issues with that setup. I also run an outrunner with mine, but only have a 138600 rate. Both are sensorless.