Irons upgrade - Ping G30's ?
From what I've seen and read you will probably not see much difference between G20s and G30s in terms of distance until you go to say 5 irons and lower, where you will get a few extra yards. However the forgiveness is probably better on G30s, but obviously harder to quantify.
But I like G30 irons as they are a well engineered club that does not have to rely on too much marketing guff to sell them. But as Rooter says go out and try as many as possible. As long as you are using comparable lofts they all kind of will hit it the same ish distance. But if you compare say 7 irons, chances are the lofts will be different between manufacturers, so you will probably present different dynamic lofts and they will go different distances.
So the choice will be more down to the look and feel and what appeals to you aesthetically. And how much you value your clubs being the latest and greatest before a new model comes out and replaces them.