Eh, the difference in size is more than marginal. When you consider that Sulak has superior mobility you realize you are looking at two very different players. This is not to say that Sulak is better at everything (I think Russo actually manages the puck better from what I have seen). Russo is a career AHLer because he doesn't move well enough for his size and is somewhat slow to close gaps in the defensive zone. Sulak brings a totally different bag of issues (i.e. decision making with the puck) to the table.
Depending on where you look, it seems the difference in size is a couple of inches and ten pounds. Unless Russo was a midget, that doesn't really bother me.
I just don't see an NHLer in Sulak, at least nothing really above what I think Russo could have held down (3rd pair). They have different strengths and weaknesses, but you're still looking at a depth guy/AHLer.