Here's Apple's current iOS product lineup:
A4 Devices
* iPod Touch 4th Gen
* iPhone 4
A5 Devices
* iPad Mini
* iPod Touch 5th Gen
* iPad 3rd Gen (A5X)
A6 Devices
* iPhone 5
* iPad 4th Gen (A6X)
Of important note us that the IPod Touch 5th gen and iPad Mini are still using the A5 processor. This means there is a large market of consumers who are going to be using devices with this processor for the next 3-5 years. That's good motivation for developers to support devices running the A5.
Most games support all the way back to 3GS currently. Though 3GS is starting to lose support for some of the bleeding edge apps. This trend is likely to change to the A4 devices being the low end.
So the support and ability to play most of the popular games will be there for A4, A5 and A6 devices.
There may be some differences bin the game between different devices due to each systems capabilities, but the experience should be similar no matter.
What you will see is that the A6 devices are going to provide a faster, smoother experience in comparison.