DIV, I used NPP frequently in my 20's, always with sust. I grew like a weed and I don't recall any sides at all. Of course, my body was different then and likely would respond to just about anything.
I must admit, I don't really recall the dosages, although I suspect they were in the 200-400mg range. I also had no clue about PCT or even anti-e's on cycle--I took no ancillaries at all (this was almost 20 years ago).
I'd assume it will stack about the same as the decanoate ester. Give it a try. One way to see the true effect would be to run an identical cycle that you have run in the past, only substituting deca with NPP. Keeping all other factors identical should give you a good idea of it's worth.
