DeWalt hasn't really catered to automotive/industrial so their square anvil impacts haven't been worth a damn. Fine for driving lags and screws but that's about it. The ones they make for MAC and the new DCF899 are far more powerful than anything else in their current line-up but I think that's going to change as they flesh out their brushless line. Currently though, for 3/8, Milwaukee, IR, Matco, Snap-On, MAC made by Dewalt etc...are far more powerful.
If you already have 18V MAX batteries you'd be better off buying a DCF899 bare tool and perhaps still buying the Matco. Personally Matco cordless has always turned me off with 1 battery kits and they have a habit of refreshing the line every couple years like clockwork. Don't get me wrong improvements are great but I don't want to spend $400-$500 for cordless that gets obsoleted at every turn. At $150 these complaints are moot though.