I have a 45+ and would love to compare it to my previous non plus back but since the files are not yet supported in Lightroom or ACR 4.1, I can't make a fair comparison. I am limited to C1 for the Plus files, which, at present anyway, is far behind the competition in RAW processing.
On another note, I do know that I was able to put a Hoya R72 infrared filter over my lens with the P45 and get stunning sharp, clear infrared images. With the 45+ doing the same yields dull, muddy infrared and I have to use a stop more exposure to get them....not worth doing. I haven't been able to get anyone, and I mean anyone, at Phase to tell me what the difference in these two backs is that makes IR photography impossible with the plus backs.