How much differnce is 3" exhaust compared to 2 1/4?

Other than 3/4" of course.

I hate to beat a dead horse to anyone who may be following...
but the free exhaust that I have, I've just measured to be 2 1/4". So for free I'm not going to complain. However I just does make me question how much better off I'd be with 3" exhaust if I had the choice? I do have a stroked 360 with headers.

Also, it has a H pipe. Does that really matter, or was it just some cool fad for awhile?