I had a 3rd gen until I eBayed it and bought a 4th gen on Black Friday because I'm getting an iPhone 5 as soon as tomorrow, just need to wait until my sis can source out a white Note II for herself. The only reason I upgraded was because I wanted a unified connector across my mobile devices, and between the BF sale price and the 5% cash back on my Chase credit card, I might have made money upgrading. There really isn't much of a speed difference, the 3rd gen is plenty fluid. If you can get the 3rd gen with more storage for a lower price, go for it. Just make sure you don't have to invest in a 30pin>lightning connector adaptor.
I was once an ignorant Apple hater, but their products and customer service have converted me.
Sent from my Macbook Air