Are those NF P12 PWM fans or just 3 pin. 3 pin are not controllable in Link. The fans are rated at 1300 +/- 10% may very well be the top speed(1170 would be exactly -10%). Lets hope not, but my AP15's are rated for 1850 and only get to about 1770(still within the specs).
If they are PWM, try a run of Prime95(while watching the cpu temps) and see how they do.
Now as far as cutting the fan grille, it is not that restrictive(not compared to many I have seen in the past), but that fan blades right near it cause more air noise(when the fan is flipped, you have a larger space before the blades because of the motor supports.). I can not even guess how much if any improvement in temperatures you will see.