Yeah, I'm starting to think more about that considering the pricing of the Clydesdale. Though, when my wife was at the shop a few minutes ago they put a SALE sticker on it, lowering the price to $3,100. So, $4,200 installed. Only about $600 more than the Enviro 1700 and Hampton I300. If I knew the answers to these questions I feel like I could make a good decision. Any help filling in the blanks is really appreciated.
1. Would we ever use the full capacity of the Clydesdale, or would a full-box-fire heat us out of the room?
Yes, you would be using it as soon as the temps get low enough outside. The full capacity would be used for a longer burn time, not necessarily more heat. Remember, you can run the insert fine on 3-4 splits during milder weather.
2. Can an Enviro 1200 pull an overnight burn?
3. Are the reported Enviro 1200 numbers inflated (high burn time and heat output with small firebox - see OP for actual numbers)?
10 hrs might be possible, especially in milder weather. It will depend on the wood. With the right wood like well-seasoned oak, locust or osage orange you will get a longer burn. But normally I'd expect around 6 hrs between loadings or less if it's really cold and windy outside.
4. How much would it cost to bring an Enviro 1700 surround to a local sheet metal shop to add 1/2" of thickness so we could slide that bad larry in?
Ask the installer if they will do this to get the sale. Or do it yourself. All you need to do is attach a piece of black angle metal to the back, perimeter of the surround. I suspect you could just use silicone adhesive or epoxy to do the job. Just don't paint the surface that contacts the surround.
5. Is there any chance that modifying the surround or fireplace would cause a permit issue?
No, I don't think so.