SPB Benchmark works. I've attached it below. Just be warned that it takes like 20-30 minutes to run each test. For comparison, before overclocking I scored like a 1350, after the OC I scored like a 1420 (I can't remember the exact numbers so these are from the best of my memory). Point is: Don't expect some sort of GINORMOUS increase... just a minor boost
Also be warned that the results are not always consistent
The answer is "yes and no"
While there are certain performance increases with things like list population (\Windows folder comes to mind), typing seems more responsive, and a few other things seem to be a little quicker... but a lot of the stuff you would think (and hope) would speed up sadly doesn't at all
For example: I use Sashimi to install all my programs and make my regedits automatically after every flash. It usually takes about 15 minutes to run. Overclocking the CPU does NOT make it finish even a second faster. Believe me, I've timed it. Scrolling through the manila tabs does not seem to improve much (if at all), apps do not open any quicker, and the homescreen weather animations are still slow as molasses.
I think there are many other bottlenecks at play here. Overclocking the CPU may help to some degree in a few areas and it's fun to do, but if you can't seem to get yours to overclock too much then fear not - you won't be missing all that much