milkman, as you likely have seen in my "signature", I have an RTV and a Rhino. They are completely different beasts. You pointed out one thing that actually surprised me; that is that the RTV is quiter than the Rhino. I would have expected the opposite, but that is not the case.
I generally put my RTV in "H" most all of the time. However, if I'm going to be going up a steep hill, it will run out of power in high gear. That is where I first discovered the problem of trying to shift out of gear on the side of a hill. Mine flat wouldn't come out of gear unless I shut off the engine and waited a few seconds. As you also likely read, that problem was completely fixed by changing the transmission fluid and filters. Apparently during the break in process the filters have a tendency to become clogged, and that causes back pressure on the gears, making them hard to impossible to change.
Now to your changing gear question; the RTV doesn't actually down shift when going down a hill. I believe the term they use is dynamic braking. I'm sure someone will correct me if I'm wrong on the terminology. All that does is use the engine and transmission as a brake. You really never need to use the brakes on the RTV. Once you get used to it, it's really nice. If you are going to go up a steep hill, especially if you are fully loaded, you will need to put it into low range first. Then, even with fairly aggressive tires, I have no problem with power.
However, that power is not to be confused with the power of the Rhino. On the Rhino, I can really spin all 4 tires in a big way and rocket up most any hill. I'm generally using the brakes to keep from going 40 feet high on a 30 foot high hill. /forums/images/graemlins/blush.gif I've added the "BlackRhino" CDI unit to mine which takes out the speed limiter, so my Rhino runs about 53 mph. It seems to run that empty or loaded.
As I also mentioned in an earlier post, I initially set out to buy a Polaris 6X6, figuring that it would be the best of both worlds. Two friends of mine who own Polaris ATV's talked me out of it. Neither is pleased (I'm putting it mildly compared to the way they described it) with the durability of their Polaris. When I did drive the Polaris 6X6, it was quite a bit faster than the RTV, but quite a bit slower than the Rhino. It was also heavier than the Rhino, but quite a bit lighter built than the RTV. My guess is that you would be hard pressed to get one hung up though! That part was impressive. If you run in really muddy places, it may be the best choice for you. Well, if I put some really aggressive tires on the Rhino and stood on the throttle, it likely would rip through quite a bit as well.
So, to have a real work horse that I could fuel up in my barn with my existing diesel tank and that would carry the load, I bought the RTV. The transmission (not a belt drive) and the power steering was a big selling factor for me. Otherwise, I likely would have gone with the HPX Diesel Gator. For a vehicle that would be a blast to drive, would be really quick, and could also haul a reasonable load, I also bought the Rhino. The Rhino is mean, fast, tough, and Yamaha has a history of producing some very high quality products. Sorry for the long reply, but it took a lot of thought to decide that I needed two UV's. Good luck with whatever you purchase.