I've started playing around with this very thing with my home group. I can't post a lot of information as I haven't done the number crunching, but here's what I've come up with.
First of all, I like the single class system in OW a little better than the class system in DW. On the other hand, I like the idea of it being a longer term campaign and I don't think prestige classes should be left out. I intend to go back through the information and see if prestige classes from DW can be compatible with OW.
I think the races in OW are a little over the top, so in my campaign, people play humans and mutated humans. On the other hand I think that the mutations presented in OW are a little better. I'm also not crazy about the non-beneficial mutations in DW.
As for feats, skills, equipment, etc, I allow everything provided that one source doesn't conflict with the other. When they do, the stuff in OW wins. I use creatures from OW and Terrors of Twisted Earth.
For setting information, I stick with the stuff at the RPG Objects website. I have thrown a bit of Fallout stuff in there though (vaults, Rad-X, etc.)