6490 RPM is abnormal. That's outrageously high...for any sized fan. Half of that is about normal during load, and around 2500 RPM at idle.
Your temperatures are normal though, no problems there. Seems to me that your motherboard isn't lowering the voltage to your fans to suit conditions. 6490 RPM is overkill.
What motherboard do you have? And had you done any BIOS updates recently?
Also, you might want to check your settings in the BIOS for anything related to fan speeds. It might also be a good idea to verify the RPM and temps in BIOS (if the monitoring feature is there) just to make sure fanspeed hasn't read it incorrectly.
Try resetting the BIOS, by removing the battery and or the specific jumper on your motherboard (refer to your manual).
Might be your fan as well. If it's your case fan, then check to see it's plugged correctly and that no wires and pins are damaged.