I agree that a physical DM is not really necessary if you can circulate the ball quickly and cleverly, which makes you hard to press (yes, I think Barca would do very well on a wintry night at Stoke). However, the likes of Chelsea traditionally always pummel Arsenal by being both decent passers *and* physical specimens who just batter them. I actually think the new-look, fully-fit Saudi Sportswashing Machine would do very well against Arsenal too - Cabaye, Tiote, Sissoko are not only technically sound but very tough. Southampton are a very decent pressing side under their new coach too.
I don't really care so much about getting more muscle or pace in our team - I think what we need are more technical, faster passers who play one-touch football, along the lines of the gooners; Holtby and Ade are a good start, but I think we need some genuine continental types in the CM and FB positions.... players who can read the game and shine on the ball as much as off of it. We're good at pressing the opposition off the ball these days, but for long periods of the game we struggle to retain it. Part of that means we need better movement (note how we pull up after giving the teammate the ball, whereas United speed up their runs) which can be coached into the team, but the other part is the technical ability and intelligence/vision of the passer.