I don't have an Anthem (yet) but have gone through them thoroughly before writing magazine articles and a review on my website at www.rvcruzer.com/2012_anthem.php
- which might answer some of your questions. I also have a 2007 Allegro Bus 42QRP so am familiar with the two.
The Anthem wins, hands down when it comes to insulation.
As a Phaeton owner you must already know, Tiffin is having issues with rotting wet bay floors and is replacing them with a 3/8" thick plastic floor that has zero R value. When they took care of mine I made sure to add heat plates beneath the fresh water tank. Enterga also relocates the water pump to a warm wall instead of on the cold wet bay floor like Tiffin does. Even with my AquaHot running, I still cracked one fresh tank in 10 degree weather. Entegra's wet bay is much warmer, has better heat distribution, better floor, better sump pan, and a relocated water pump and filter.
Entegras wood over steel floor is R-33, which is unheard of in the industry. They place additional reflective foil behind the batt insulation in the walls, whih are thicker than Tiffin. They insulate the front and rear cap which Tiffin does not. In fact I has to reach back about another foot when I had the front TB out just to find where the insulation started. Add a 3/8" plywood layer between the fiberglass roof and aluminum trusses and you can see why the numbers add up.
At Indianapolis this summer Leann and I went through various motorhomes and checked cabinet interiors. Many cabinets get the opposite treatment when the hot summer sun is out and you really can't store food (dry goods) in there because the cabinets get quite hot. You need to leave a door open or have a louvered door in order to get the heat out and the air conditioned air into the cabinet. We found most of them to be quite warm (we wanted to try Newmar but they were inside the building so it wasn't a fair comparison). But Entegra cabinets were much cooler. So what keeps you warm in winter will help keep you cool in summer.
Some motorhomes are not that well suited for cold weather camping (we both have one of those), while some are better suited. In my opinion, Entegra sets the standard.