I have done exactly what you have described.
I didn't want the added noise of a cat back system, so i only upgraded the dump and front pipe. I did not expect to get a significant power increase but was hoping for better response as the stock dump is extremely restrictive.
As expected, power does not appear to have increased significantly, but I am getting better response, especially from a standing start.
In general, i'm quite happy with the upgrade. But if you are looking for a real power increase and don't mind the added noise from a free flowing system, upgrade the cat-back system first.