I'm no expert, but if I'm not mistaken I believe the second test is mainly for your CPU. It stresses the capability of your CPU to push out graphics instead of the video card. This is why your frame rates are a lot lower. I only ran a couple of those tests and that is what I took away from it. This would also explain why your overclocked CPU froze during that specific test, not because it was overclocked, but maybe because it was overclocked too much and the test made it work too hard.
That was my two cents, but I'm sure someone else will probably make me look to be the fool. Like I said, I am no expert. Hope this helps.