There is a point where more advance doesn't provide any useful benefits. There are lots of variables in play and without a proper dyno, it's hard to know what timing provides the most power or torque (whatever you're trying to optimize for). For most of the 17.5, 21.5 and 25.5 motors I've dyno'd the optimal timing is around 50 degrees, but some motor brands peak lower. Timing also affects the power curve. Power is a curve, not a line, based on motor RPM. If you're running a track where you're spending most of your time at full throttle, you'll add more timing. But if it's a very technical track where you're spending more time in the mid range or if there are jumps you need to accelerate to clear, you need less timing. You're shifting the RPMs where the motor generates the maximum power.

Where are you seeing 8.5 amps?