Here's another update.
I've been running the RX8 ESC on 4s2p A123 in the GTP geared 51/20 with the 4000kv hacker. Everything was okiedokie, but topspeed was not the same like the 6s1p A123 pack. So I ordered the 25T pinion from Mike and the GTP became an animal again...for like 2 minutes. I thought the RX8 smoked, but all was good and the motor plugs were all unsoldered. Soldered on 6.5 connectors instead and ESC kicked butt again. I need to datalog the sucker and see how many amps it's consuming.
Motor wires are 12awg, and battery input wires are 10awg.