Hope the original poster is still at it. I had cleared Inferno 5 for the first time after faulting out twice around when this thread was started. Didn't even bronze it.

A few days later I decided to try again, got a bronze time around 21 minutes, tried some more. Told myself that was my limit, I just simply didn't have what it took to improve beyond that.

Just today I find myself on Inferno 5 again, chipping away time and faults down to the point of nearly silver, when finally the miracle run happened!
My adrenaline was pumping so hard at the end I could barely keep my bike on the wall, but I finally got a grip (heh) and pulled it off in just under 7 minutes.

Point being, don't give up. I thought I may have hit my limit so many times but never gave up on the idea that I could improve, and you will as long as you stick to it.
Ain't nothing to it but to do it.

Now if only a can-do attitude was all it took to clear ninja tracks...