In my opinion:
Despres is better than Engelland, Niskanen, and Bortuzzo. Niskanen is a number 5 and Engelland is a number 6, a number 7 on good playoff teams. Bortuzzo isn't better than those 2, but he will be. Niskanen has been making a lot of mistakes lately and every time they try to dump him up with Letang it works for like a game then he turns bad. This is what I would do right now:
Letang - Despres, Pens are 11-4 with Despres playing in the lineup, he's a stud..I would leave this alone for the rest of the year.
Orpik - Martin
Engelland - Bortuzzo - Nice gritty bottom pair, they don't need to play that much 5v5 a night so it shouldn't be a big problem.
Niskanen - decent all around defenseman that can fill in where needed. He should be number 7 at this moment.
Or sit Engelland for a bit. You know, what is he now? 28? He's obviously peaked as a bottom pair. I think Borts could be top 4, but this is screw with Despres/Bortuzzo's development and I don't like it.