While waiting to see if we have any direct replies, you might try searching for past threads and maybe turn up somebody you could e-mail about their ranges.

Having trouble turning up threads here with the internal search function? For the present, it seems to me that the Houzz engine is as hit or miss as the previous Gardenweb one. You might have better luck by going out to Google, Bing, Ask, or whatever. Try a search string like "gardenweb + nxr + 48-inch range" for NXRs, "gardenweb + Blue Star + 48-inch range" for Blue Stars, etc. Add the word "propane" to the search string to narrow that even more.

I don't recall seeing any discussions here about the 48" American Range.

Are the 48" Miele's even shipping? Last I recall hearing about them (from a post a couple of weeks ago) was that a display model was expected sometime soon at a showroom in Beverly Hills.

http://ths.gardenweb.com/discussions/2812367/new-miele-dual-fuel-gas-range-experience

My recollection is that most of the NXR discussions here have been about the 30" and 36" ranges. I only recall a couple of posters mentioning the 48" version. IRC. One of them had some pretty big problems with the range initially delivered and also posted on chowhound. According to a follow-up posting the other day on Chowhound, the problems got taken care of last year after the poster contacted Costco and he/she has been very pleased with the range since then. Here's a link:
http://chowhound.chow.com/topics/685147?page=3

If you have access to Consumer Reports online, there was a disappointed buyer of a 48" NXR who posted a review on CR's report on the 30" NXR model. If you haven't already checked Costco.com, I think there are a couple of positive reviews there under the page for the 48" model and I think there was a negative report on the 48" model posted on the page for the 30" NXR model.

I do not recall any specific discussions of propane conversions/versions of the above 48" ranges but I think there have been some postings on LP set-ups for 30" and 36" models from AR, Blue Star. and NXR.

I can't speak to a 48" range, but when we remodeled our kitchen in 2010 we went with a Bluestar RNB 36" 6 burner range.

After a few months the oven door began to creak when trying to open it if the oven was on. There was apparently a problem with the hinge. We sent an email to Bluestar and were shipped a new door within 4 days time.

We couldn't be more pleased. It's been about 4 1/2 years and to date no other problems at all.

If you use the search terms "test drive 48 blue star this week gardenweb" you'll find my review from dec. 2014. I'm on my tablet and don't know how to give you a direct link.

I've had my 36" RNB with griddle for just over two years now, and absolutely love it!

No issues thus far, it's truly a solid workhorse piece of equipment. Burners are the best I've ever cooked on, and the griddle is a dream.

I do wish the broiler was a bit larger, but I don't broil all that often, so not a big deal for me.

Love my Bluestar 30" RCS range..... favorite tool in my kitchen. No issues with anything, so far....