300 Hp, i would have to see it on a dyno. The most power that has been done is from CPS, (Calibrated Power Solutions) 200 Hp and 400 ft lbs torque. And that required a injection pump up grade at a mere $2600.00, and a turbo upgrade, $800.00 and a intercooler upgrade, $900.00. I just picked up my Roxor yesterday from CPS. I borrowed them my Roxor to test new performance upgrades. well it turned out very well 160 Hp, and 345 ft lbs torque. Really goes nice now. Yes i have the dyno results to prove it. To reach that much power required a turbo upgrade, intercooler upgrade, and a methyl alcohol injection kit and i have a 3" custom exhaust. With the meth injection off it makes 132 Hp, and 283 ft lbs torque. So I'm pretty sure seeing 300 Hp is a nice dream but very hard to reach and will require a lot of money.
As far as melting a piston, if you keep EGT's down the pistons will be fine.