RealVNC works really well assuming you have RealVNC on both ends on the iPad, iPad 2, and iPad 3.
The application simply named "Desktop" does a pretty good job as well especially if you install it's package on the host machine you are connecting to. You get a substantially more "robust" experience by doing that and using the Google integration.
I picked up an iPad Mini on Friday but been slammed and haven't had a chance to mess with it on that. I fully expect the performance to be comparable to the iPad 3 and iPad 2 especially as seeing as performance in general between those two was virtually identical.
Just about everything out there right now for the iPad is targeted for the A5 processor since this is what the bulk of devices are running. In gaming you may see a difference with the iPad 4 and iPhone 5 but generally speaking outside of application switching across several apps over and over again the experience is fairly identical.