Heck, we need to fish together! Sounds like we enjoy the same style of fishing. Mid to late July is a smart time for your trip if you don't have time to sit around waiting for the rivers to clear. Runoff will be over most everywhere, but there will still be some good hatches going off. Like I said before, it's been a while since I fished out there, and conditions change, so take my recommendations for what they're worth, but here's what I might like to do if I were out there this July.
Those Missouri fish you caught were pretty darn impressive and if I were you I'd be tempted to go back for some more of that action. Only problem is that wading just isn't the best way to get at those fish. You really need a boat to take full advantage of that big water. I've only fished there a handful of times and it looks like you had more success than me, anyway, so I'm probably not the best person to give advice about it.
The Bighorn, way over in southeast Montana is probably the next closest thing to the Missouri - big water and big tailwater fish, but there are a lot more side channels in the Bighorn. It's primarily nymphing, but you can always find a few risers in the eddies if that's your thing. The river channel around Cottonwood Camp (Three Mile access) is really cut up and is great for wading. It's just high plains out there, lots of horses and hay. It's pretty but not like western Montana.
I'm really partial to the upper Madison just because I know it so well. The stretch of river below Quake Lake usually clears around the first of the month and is ridiculously predictable by mid-July. It offers some of the most consistent nymphing for 15 to 20 inch browns and 'bows I've ever found. The upper Madison Valley is pretty, but it's not particularly remote by Montana standards. There are homes built on some stretches of the river and it sometimes feels like you are in somebody's back yard, but who cares when you're catching lots of big fish! If you want some variety, and you have a float tube, you can chase big sipping rainbows up on Quake Lake in the evenings, too.
If you're looking for more solitude and you're not adverse to some physical exertion, you might consider the Black Canyon of the Yellowstone in the park. It's a bit of a hike, but once you leave the trail, you probably won't see another person the rest of the day. Just you and big Yellowstone cutthroat that rarely get fished over. The goal is to catch the Salmonfly hatch, so if you hike in make sure you got some big orange Stimulators or Madame-X's in your box since the fish will key on them for quite a while after the hatch is over and nothing is finer than big wild trout on 2 inch dry flies. The scenery is stunning, but equally dangerous. It's the middle of grizzly country, the canyon walls can be treacherous, and if you fall in the river, it'll be your last fishing day on this earth ...but it's totally worth it!
If you think you might want to head in any of these directions I can give you a lot more detailed information (like the easiest way to access Black Canyon, fly patterns, nymphing techniques and the like).
Here are some shots of the wife fishing Black Canyon.
[attachment=0]Black Canyon Cutt.jpg[/attachment]