I went through the same thought process with the hole for the gearbox, then decided to go for the 775's just because there rated voltage is 18v and i wanted to run 5s anyhow... and with the 98mm wheels on 16:1 they stay relatively cool, and spin the wheels easily... not sure what differance running 125mm wheels will make... might be a bit fast? I've turned my turn rates down to around 60% to make it controllable, and ive got way more pushing power then i need really.