I think that if you set 60Hz in nvidia control panel than you actually had it. Real frequency you can see in native monitor menu, if there is an info page.
It's realy nice test, man! :)
Interestingly, all differences are multiple of 10 ms. That meens you run the test at 100Hz, right? Native frequency for LCD monitors is 60 Hz, and AFAIK even when they report 75 Hz they actually work @60Hz and interpolate signal from 75 to 60 Hz. That introduces...
Try 1/1000 s (1ms) shutter speed, it should be more than enough. ISO value you can choose after a few tries. Digital noise caused by high ISO values is not an issue because the main goal is to get readable timer values.
BTW number of readable shots should be rather great (~20) to statistically...
swingdjted, a description of input lag and testing procedure you can find here:
http://en.wikipedia.org/wiki/Input_lag
and here:
http://xbitlabs.com/articles/monitors/display/lcd-parameters_7.html#sect0
Here is test timer:
http://tft.vanity.dk/inputlag.swf