Three man midfield, Petrov and NRC holding, Sidwell pushing forward, to me that looks nice and balanced. Petrov and NRC are both tacklers, NRC more so, but Petrov can pass better, and Sidwell can do a bit of both and can get forward and shoot.
But I'd still prefer 4-4-2 with Petrov and a new midfielder in the centre.
I've said for a while, without really being responded too that I don't think Petrov can play in a simple 4-4-2, because he's not the creative midfielder and nor is he the midfielder dominator what teams need. When your below the top 4, I personally beleive you need a midfielder with huge energy or play 4-5-1 / 4-3-3.
The midfield you pointed out would balance each other nicely, but I do remember our best football coming in the 07/08 season with N-R-C and Barry in the middle. N-r-c that year made the most tackles in the Prem and as soon as we won the ball, we sprung an attack. Last year with Barry and Petrov in a 4-4-2, it was just pressure on our goal as the only time we won the ball back is if they mis-place a pass or a bad cross, or a shot because we just didn't tackle because Barry and Petrov don't.
I think N-R-C and a really creative midfielder who can blooming pass, say Defour would really bring the exciting football back!