RE: hawk pro upgrade???
Why bother, for less money you can get the Century Raven 50 that will outperform a fully blinged (that includes all the items that come Stock on the Raven 50) Hawk Pro.
That being said, I do not know what radio equipment you are using, but the HAWK PRO is a very good heli and long enduring heli basically right out of the box. You have not indicated what radio, servos and gyro you are using on yours. I have found these (along with the stock muffler) are usually the items that will limit the performance of a 37 powered Hawk Pro. So if you are planing to spend money on it, this is where I would first look.
Better servos and gyros will also be with you a long time and can later be used in bigger and higher powered helis.