People always say the same crap after a new iPad is released. "The iPad 4 has the new A6X and they bumped up the RAM from 512MB to 1GB. It will easily last you for 5 years until 2017". Meanwhile those same people probably already upgraded their iPads multiple times in between 2012 and today.
Forget all specs, general rule of thumb is first 2 years will have lightning performance, the 3rd year will have good performance, the 4th year will be usable but you'll want to upgrade, and by the 5th year you will be begging to upgrade.