I've owned 2 Newmars; a 2017 Dutch Star 4018 (450/1250 HP/TQ 8.9L ISL) that I bought new, and a 2019 Mountain Aire 4018 (500/1695 11.9L ISX) that I bought about a year old. Nothing touches the Newmars for interior quality, the way they drive (with their exclusive Comfort Drive) etc. until you get into the $2M+ range of Newells and various Prevosts.
The King Aire is, or course, the King. However, like most things you pay the biggest premium at the top-top end. If you want a 45' Newmar with the big 14.9L 605/1950 HP/TQ ISX then I'd look at London Aires. You'd be hard-pressed to really pick up on the minor differences, and if you want a little nicer than a LA but still under the KA could go with an Essex (the lineup goes King Aire > Essex > London Aire > Mountain Aire > New Aire in the Luxury line).
When I got my Dutch Star, which isn't even a Luxury Coach in their book, I was super happy with everything in terms of decor/fit/finish etc. Yes, it had little problems to work out but I was never left for wanting more build quality or anything "fancier." I really loved it being a 40' coach with a (passively steered) tag axle, something larger than the typical 6.7s you find in shorter As, and Newmar quality, but it could have used a little more power. I weighed in one time on the way to Idaho with the coach and my 20' stacker with my Potter and a 2 seat RZR along with tools/spares/camping stuff whatever but I had *not* yet filled up the stacker's fuel/water and IIRC I was around 53k lbs. 450/1250 sounds like a lot for "just" a 40' coach, but not so much when the coach itself was over 40k lbs.
I sold the DS because I thought I could go back to a 5th wheel, that lasted less than a year I think? Then I went to that Magnitude I mentioned, and I really did like it but the interior quality and fit/finish are "toy hauler quality" not anything like the Newmars (same is true for my current Nexus, it's maybe even a hair worse than the Thor was, but better in other areas like the chassis itself and metal "house" construction). When I decided to buy at the Motorcoach Country Club I "needed" a Class A again.
I always loved the size and floorplan of my DS, and form 2018+ Newmar started offering that exact floorplan on a Mountain Aire. With the DS you get a Freightliner or a Spartan K2 chassis (mine DS was on the FL). With the MA you get the full-on Spartan K3 that everything up to and including the King Aire uses. You also get the "small" 11.9L ISX at 500/1695, and you get the Allison 4000 (the DS was the 3000). The MA gets you into Silverleaf and a bunch of other cool stuff too, and only weighed a little bit more (1-2k lbs IIRC) than the DS in the same floorplan, so the power difference *was* noticeable.
Anyway, not saying I wouldn't rock a KA... and as weird as it sounds they are sort of a bargain compared to spending $2-3M on a Newell (though, Newells are next-next level... Newell had 2 new units on display every year at MCC and wow, when you walk them you "get it"), but if you're serious about Newmars I'd check out some of the "lower" models.
-TJ
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