Metcalf, I would suggest that the difference you are attributing to front vs rear is actually the difference between an automatic locker and a "selectable" locker. An "automatic" locker always allows for a wheel to over-speed without consequence, somewhat relieving driveline bind in a turn. An engaged selectable locker is, in effect, a spool. A spool adds a LOT more steering resistance than the auto locker, regardless of which end it is installed in.
My experience is that in rock crawling and other other technical low speed wheeling, when going from uphill to downhill (or drive to coast, or any other reason for torque reversal on an axle shaft), an auto locker of any kind can occasionally release and pop on one axle as torque on the axle shaft reverses. This can result in a bit of lurching of the vehicle as a bit of rotational "slop" on the diff is taken up. A spool or engaged selectable locker will not do this. Perhaps this is some of what billiebob was referring to, but I do agree that he's also still attributing "limited slip" characteristics (like being assisted by brake torque) to automatic lockers, which is incorrect as Metcalf and MTVR pointed out.
I bet the OP is bored silly with our technical discussion at this point, but hopefully it'll answer questions for others too!
My front automatic locker behaves night and day different based on the REAR axle. If the rear axle is open the front axle is happy as a clam. You can't really even tell the front is locked other than a bit more return to center feel in the steering wheel when on the power ( and I have very wide tires and wheels on the flatty that are run at 1-5psi off road ). No pops or windup at all.
With the rear diff locked ( effectively a spool as you mention ) it completely changes the characteristics of how the chassis behaves. You can tell it wants to go straight much more. It doesn't really increase steering force too much, the steering just becomes less responsive and the front tire gets folded over more as the vehicle is trying to go straight.
Personally, I think it boils down to the rear axle always wanting to go straight and the front axle wanting to go in the direction you point it. This is why I am a big proponent of 'front locker first' contrary to how most vehicles are set up. For me, that just works WAY better all around. The largest speed differential is actually on the REAR axle in a tight corner. I think the open rear diff allows the vehicle not to 'push' as much as a locked rear diff with an open front diff, especially when trying to climb and turn at the same time. I usually refer to this at the '3-wheel drive' problem. It is that odd time when you need more than open/open but less than locked/locked AND vehicle maneuverability is still very important. Going in a straight line with lockers is easy, the nuance is when you have to maneuver the vehicle when open/open is not enough. There is also some interesting stuff going on between the front and rear axle speeds in a tight corner....that adds another layer of weird.
For me, front and rear automatic lockers still have too much 'push' in 4wd. Front wheel drive only can help, but then you are back to 2wd....not 3wd.
I don't mind selectable/selectable, but for me it just doesn't work as well for what I do. I get REALLY annoyed having to lock-unlock-lock all the time when trying to tightly maneuver the vehicle when dealing with the '3-wheel drive' issue. Selectable lockers, especially in the front when dealing with scrub radius bind, don't like to unlock right away.
