2500 should be fast enough. Are you running any other case fans? Have you tried reapplying thermal compound?
I only have 2 fans one in the power supply and the one ont cpu, when i go into easy tune 5 it has a warning on my cpu and my fan. Im not sure what a thermal cpmpound is i dont know much about computers i just like to play them :P
The thermal compound is a paste that is used between the mating surfaces of the CPU and the heatsink assembly to enhance thermal convection.
Is the fan spinning freely? Does it run any cooler with the case open? If it does run cooler with it open you might want to add a fan to the front of the case to draw air in, and a second on to the rear of the case to exhaust the air.
Is the heatsink fan assembly firmly mounted, no movement?
That is fast enough for most cooling. But a replacement fan is so inexpensive... $12 to $20, that you can easily replace it. The combo units with heat sink designed for your particular CPU are much better for just a few dollars more. Get a name brand: Cooler Master or better designed for gaming.
If your temp is 65 centigrade, you don't want to run any hotter...
I would add a couple of case fans, also very low priced... one on the front... one on the back... to keep the air moving... and be sure you keep the heatsink and the fan in the power supply blown out with a difluoroethane gas such as Dust Off or equivalent. Do not use compressed air or a vacuum cleaner.