It has far more transisitors than the 4th gen which allows for higher speed caches, also More transistors means you can put in more parallel execution units. Bigger cache. Deeper pipelines. To build more complex coding and execution power, it's is compulsory to have higher number of transistors.
A smaller die size, reduced TDP and and a cooler processor (not that it's really amazing of an enhancement)
Frankly, Don't see the point in an 5th gen, the 4th gen are more than capable to last for a while. They are really powerful and formdidable processors. But as for the sake of future proof, the 5th gen should do good.