OP, you have a very nice revolver. This thread made me curious about its value, so I searched through closed auctions on gunbroker. I think
@Ratshooter did a similar search, but we must have used different search terms, since my results are a little different. I found only one 45 Colt Mountain Gun which sold at auction recently, and it went for $940 in December. There is also an active auction which has one bid for $849 and two days left on the auction. I will be surprised if it does not get several more bids. There are also several more 45 Colt Mountain guns on gunbroker with starting bids at around $1100, and which are not getting much interest. However, that does not mean that a lower priced auction could not go past that point. Auctions are strange sometimes.
I have not put things for auction on Gunbroker, but I have a close friend who has done it quite a bit, and he puts everything at penny start and no reserve. People who actually want to buy seem to pay the most attention to those auctions.
Regarding the 45 Colt Mountain Gun, it really is a very desirable revolver, but you need to find the right buyer to get the right price. There are lots of people who like 4" big bore N-frames. But there are some people who really prefer mountain guns, and there are some people who really prefer 45 Colt. So there are some people who think that your revolver is one of the most desirable Smith's ever made. But it may be hard to find those people. Anyone who says, "I like that gun, but I would not pay more than a standard 4" barrel 44 magnum" is not really interested. That person wants a big bore Smith, but doesn't see anything special about your gun. As an example, I think the 357 magnum 686 Mountain gun is the most desirable L-frame Smith ever made. I am not the only person who thinks that, and prices reflect it.
So I am wishing you luck for finding the right buyer who will pay you a fair price, and who will really enjoy your handy and well balanced revolver. I think that the $800 you mentioned is more than realistic and might even be a price to a friend. If I was putting it on consignment in a well traveled store, I might put it at $1100 so there would be room to bargain down to $1000. With most consignments that would get you $800 or a bit more. However, prices do vary by area, and they are pretty high around me, so consignment might not work well other places. Good luck.