Increasing the GPU frequency of the GTX 650 Ti a little will not change its performance by much at all. It's too extremely memory bandwidth bottle-necked. It'd be faster if they brought the GPU down to 576 cores at the same frequency and bumped up the memory interface to 192 bit at the same frequency. The GTX 660 and GTX 650 give very conclusive evidence for this.
[citation][nom]lhughey[/nom]You don't say it often, cause you hear it all the time! Sorry, I couldn't resist. But seriously, this is another example of how competition is great. I just wish they would do this for the 660ti.[/citation]
The same is true for the 660 Ti. It's GPU is so memory bandwidth bottle-necked that increasing its frequency a little own't make much difference whereas increasing memory performance does make a difference (the GTX 670 and 680 prove this quite excellently).
If Nvidia wanted a decent improvement in either card without changing the hardware, then the best option would be to make a new reference specification with better memory for the 650 Ti (and also the 660 Ti if they wanted a higher performing version of it). Unfortunately, except for the unlikely scenario where Nvidia would also require better memory binning as well, I find it unlikely that this would help the overclocking community in getting more card options in this price range.
A higher GPU frequency wouldn't hurt, I'm just saying that it won't make much difference on its own, at least not unless it's a very big change.