Well, I figured that if a handheld could get close to current consoles, surely a tablet would be capable of the same. I'm not really familiar with anything tablet/pad related.
First of all, The PS VIta isn't as powerful as the 360 or PS3. Given it's limited screen size, it's apparent power does increase, but even then It's not as powerful as a 360 or PS3. Second of all, there's the underlying implementation of software, and some of Android's way of doing things (specifically: http://nfarina.com/post/8239634061/ios-to-android#animation) makes it less optimizable, which will take another hit to performance.
I'd say this is around PS2/Xbox original level.