I have a HO 6 speed with 4. 10's and pull a 10K 5er. I really like the 4. 10's for towing. I can stay in 6th gear all the time unless I'm climbing real mountains. The axle choice has as much to do with how much you drive empty as it does with what you are towing. Since I rarely drive on the out-or-town freeways empty, the 4. 10's work well for me all the time, and they don't affect milage as much as many think it does.
I've heard a lot of members with 3. 54's say that they would never get 4. 10's, but rarely heard someone with 4. 10's say that they wish they had 3. 54's instead.
I am curious for members who pull loads of 10K or more in hilly terrain, what gear do you normally tow in and at what speed? I really am looking for responses to this, so let me know. It seems to me that if you want to keep your speed around 65 MPH, you are either at 2500 RPM in 5th, or 1800 in 6th. With the 4. 10's, I can tow at 2200 RPM at 65 MPH, which works great.