So I am toying with the idea of running a spool in the front of my XL7 since the only rear locker available is a welded diff; I feel like it's a better compromise to be able to "select" the front locker by either running in 2wd or else only locking one hub. I'm just wondering how many people have tried driving in 4Hi with only 1 hub locked, say for instance on a snowy road. I'm curious how it would handle.

Interesting idea.  I’d guess it would handle terrible because same problem exists of wheel speed just not as bad with one unlocked. 

I have considered the same thing olija, except welding the front diff.  My guess would be that it would be a little wonky, primarily depending on which direction you were trying to turn.  My neighbor had a K5 mud truck on 38's with a big block.  That is the route he went, welded and only locking 1 hub.  When he was trying to run a "bounty hole", and knew it would only be straight line, wide open running, he would lock both up.  He had too much tire and horsepower for any kind of turning with both locked, and anytime he tried running very hard while turning it would break an axle shaft.

Hmm, yeah, that's what I'm concerned about. I've got the steel front housing but the CV's and the actual differential unit itself are still pretty small, and they were only designed for about 90 horsepower and ft-lbs originally, I'm running 185 of each with the 2.7 V6...so I fear that even if I am driving it cautiously it will be too much for that poor axle.

It's a tough call though, cause what's more abusive on a driveline? Loading and unloading axles as you bounce and hop your way up a loose climb, or having more traction than your axles can handle and demanding that a single tire pull the entire vehicle up if it's the only one with traction? I'm still undecided at this point...most people are only running a locker in the rear but I don't have that option.

I have been running more than 6 years on 33's, with a 2.7L V6 without any problems with my gears or axles.  My automatic absorbs a lot of the shock, and I am only locked when it is required.  But I watched a 1.6L bust his Ring & Pinion with two short hops on slick rock. 
I wheeled with a friend and his tracker on 33's that was welded on both ends.  After every obstacle he would jump out and unlock ds hub until next obstacle, what a pain.
Going to larger tires is harder on the gears and axles, especially with good traction.
I have ran in deep snow with both ends locked.  I had better traction and control than running with the front end unlocked, like you were asking.  I have ran at 60 mph that way, and then when the snow gets thin I drop the front locker out (same as unlocking one hub).