Ideal iMac For programming (and some photoshop) I am going to get a 21.5" iMac. It will primarily be used for Android, iOS, and web development, but may occasionally be used for some photoshop. Any other uses I have for it will be insignificant (such as web browsing or email)

Between the two 21.5" models on http://store.apple.com/us/buy-mac/imac, considering my primary uses for it 


Would I likely notice any performance differences?
Should I expect the higher model to last me much longer than the lower model?
Will the lower graphics affect my ability to use Photoshop efficiently?
Basically every iMac shipping today has plenty of power to handle your developing and photo-editing needs. When it comes to lifespan, there is virtually little to no difference. Finally, unless you're working with intense 3D graphics, you should be absolutely fine with the base model.