Well, it has been very hard to find any difference between shots with Sony Alpha 900 and Sony Alpha 99 although one has a DR of 12.3EV and the other is around 14EV (according to DxO). I have shot digital since 2005 and had early Minolta, most Sony's and also a Phase One. Also I love high contrast.
Still I have not found a lot of images that were exceeding the dynamic range of my cameras, and I found very few cases where HDR shots came out better than well processed raw images. It took me a few of months of testing to find an image where the DR advantage of the Alpha 99 was clearly seen, that was a dupe of a very contrasty Velvia slide in a totally dark room. If the room was light enough so I could see the camera the difference disappeared. [because surround light is reflected on surface of the slide].
Another factor is that in most situation there is some lens flare, that limits contrast at the image plane.
That said, I feel the P45+ is a bit problematic with noisy shadows.
Leica M lenses are not retrofocus designs and they will probably have issues with lens cast, and will also loose sharpness as the optical package in fron of the sensor is optimized for lenses with lower ray angle. Theory says that and also most test reports.
This is an image from the Alpha 900 (12.3 EV DR)
Raw histogram: see below.
I would think the A7/A7r is an excellent camera, I may even consider it myself. It works probably very well with a lot of lenses, but many folks want to put Leica glass on it, and many of those lenses don't work that well with modern sensors. Sony cameras are built for Sony lenses. Offset microlenses are optimized for Sony lenses, IR-filter is probably thick. The OLP-filter on the A7r is replaced with optical glass of equivalent thickness. That gives astigmatism on "Biogon" type designs.
All Leica glass is not created equal, by the way. Todays optics are quite good actually, at least the better ones and a high resolution lens shows all weaknesses a lens may have. Check this article: http://tashley1.zenfolio.com/blog/2013/4/leica-m-240-with-35mm-f1-4-fle---some-observations
I think that all those things are worth consideration before spending your money.
I would also suggest that this article is offering some insight: http://echophoto.dnsalias.net/ekr/index.php/photoarticles/63-lot-of-info-in-a-digital-image
Ps. Main reason I shoot the 1$ bill is that it's available to most people, so anyone can reproduce that part of my testimage. Some folks survive on something like five $US a day, but I guess those folks have other concerns the DR on the A7r.
Overrated ? Dynamic range is one of the D800's hallmarks and the Sony is supposed to improve on that (though I doubt it will be by a full stop). Considering the only alternative for shooting wide angle retrofocus leica lenses is with a 13.3 Evs $7000 Leica 240, the a7r is a pretty big deal. Stitching 36MP images from Canon TS lenses, holding the camera vertically and doing full resolution 70MP+ panorama sweeps with leica glass... Probably ok ? You've shot one dollar bill too many