The issue with the 5-3-2 is that it puts a lot of pressure on the wing backs, as they have to be capable of providing a lot of your attacking opportunities and defending well, and covering all the ground that requires. Freeman, imo, is capable of this. Lafferty, I'm still unsure of, and Hussey had a fairly disastrous start (although I think he should get opportunities to prove himself as the season goes on). We also need Fleck/Basham to do a lot of donkey work, and Duffy and Coutts (or whoever) to take hold of the game, move the ball well for the wide men, and dictate the pace while creating chances for the forwards.
I think we do have the potential to make it work, whereas our issue with a 4-4-2 is going to be that we don't have the wingers to offer real attacking threat. Chapman is the only one who looks like a "traditional" winger to provide us enough width in that formation.
Personally, I'm a big fan of the system we started with against Posh, and also think that was the best I've seen this season and for a long time before it. But I'm a bit biased because when I was a kid I thought Spackman's 5-3-2 was pure genius.