Matt,
I've read a ton of posts on this subject and it seems if you want a good balance of off road and on road wheels/tires. The best combination seems an 18" wheel with a 35" tires such as the Toyo Open Country M/T's. I got the Cooper STT's because teh 35" Toyo's were backordered. However, I've had two sets of the Toyos and absolutely loved them. On road they are surprisingly quiet for a mud tire. The tread is aggressive and somewhere on this forum DRTYFN did a commentary on their off raod ability...which was very positive. Most of all, they just look hot (both The Toyos and Coopers)!
Also, there seems to be several posts regarding articulation issues while wheeling with 37's. I'd stay with 35's.
Also, I know you've had many custom wheels before but make sure the offset and backspacing is right for your Hummer. My 18" Kaotic NT-2's looked hot but they stuck out 2 inches beyond the fender. Damn Issaquah police stopped me once but only gave me a warning. Plus, with all this rain the minute you drive off after washing the truck it's dirty.
I'm really happy with the 18" Black KMC's I got. They are very easy to clean and have the right offset. Plus you can get them all day long on Ebay for $700.00! I think black wheels would look great on your Pewter rig.