To the OP just to clear up the subject. Your reporting 500-1000 collision checks. That's good less the better if you can get away with it. however Performance boost isn't really magical situation. Even when one element is improved in speed doesn't make the entire game suddenly work better. It really depends on the stress of the game on the area at hand.
We know that renderering is slow. If I have 60fps with just 10 small objects and say 20fps with 3000 objects. When the performance comes in and and the 3000 objects can now run at 60fps doesn't suddenly make the 10 small objects run at 300fps.
The same rule applies collision checks. Sure there is a performance gain, but only in situations where collisions were slowing down the system when the time taken is more than 0.015ms(time of 1 frame).
500-1000 collision checks isn't going to hang up your CPU. Where as BluePhaze 50+k collision checks will see a vast improvement.
Since you seem to be bottled necked it's not collision checks that causing the performance problem. Also I'm not sure, but I though collision cells came in after r153. I could be wrong, but it's not really the point of the post.
My suggestion is to check the debugger and find out what's bogging down your game.