Crazy, but my tt is as fast with the gtb speedo than with the mmpro with timing (22 degrees) and temps are around 100 (150 on mmpro with timing after 5 minutes) with the 6.5. Though in the sc with 13.5 the timing really hits in and makes it faster than the gtb. I guess mmpro isn't a good mod esc. And no ext bec needed with 13.5, though the gtb needs a glitch buster with the savox servo in the tt.
I put the gtb behind the motor, perfect level flight without nose diving, a much better driving feeling. I think the smaller the speedo the better for this car and easier for weight distribution.