Upload & Sell: On
I think the newer N and A versions of M645 lenses are all relatively good at handling flare. These lenses have higher contrast and perhaps better flare handling than earlier 'plain' C versions. I generally use a hood when shooting, and I have a compendium hood from my Mamiya Auto Bellows N setup that works well for tilted/shifted lenses.
The lens price database, Lens$db, has a complete list of the N and A versions (bar a couple of leaf shutter lenses), and many of the C versions. Note that the N versions also have a C in their name, but not the A versions, no C that is.
The image quality at full shift is generally very good, the 55N is a bit better here than the 35N (mostly due to vignetting), but they're still usable. Of course, you often don't need full shift on the Mirex, even for shift-panos. Most other shift lenses only go to 12mm, while the Mirex goes to 15mm. With the Mirex at 10mm to 12mm shift, there's no significant image degradation, especially when compared to other shift lenses at 10mm to 12mm shift, which is their max movement.
All of the A-series lenses are of note. They're as good as anything else available, including "35mm format" Zeiss and Leica (except different, of course). The A 120/4 Macro and A 150/2.8 are real bargains, as they're far less expensive than the other 'Alternatives'. The A 200/2.8 APO is fantastic, but unfortunately it's price has been steadily rising for the past few years. The A 300/2.8 APO is also fantastic, but it's rare and not better than the Canon 300/2.8L IS. I've owned fifteen of the twenty-one different M645 prime lenses shown in Lens$db. The only 'notable' ones I haven't tried are the 24/4 Fisheye and 500/4.5 telephoto. I now own the Canon TS-E 24/3.5L II and EF 500/4L IS, so these last two 'notable' M645 lenese are no longer on my radar screen.
I normally use the 35/3.5N, 55/2.8N, 80/2.8N, and A 150/2.8 with the Mirex for T-S images. Although, they're just as good IQ-wise 'straight up', as most of my Canon L primes (at common apertures). I normally use the 80/4N Macro, A 120/4 Macro, and A 200/2.8 APO 'straight up' with fixed Fotodiox Pro adapters. I use the Auto Bellows N system when I want to do tilt-shift macro shooting.
The N series enses for all focal lengths from 35mm up to and including 80mm are all really, really good. The 45/2.8N is an excellent lens, too (on par with the 35N and 55N), but I sold mine because I always went to either the 35N or 55N. The C 50/4 Shift is very nice, but relatively large and heavy. For a while I toyed with the idea of using it on the Mirex for supershift, but I sold it instead.
The C 150/3.5N, C 210/4N and C 500/5.6 aren't anything special. The IQ of the C 150/3.5N breaks down with moderate tilt and shift past about 8mm (the A 150/2.8 does not - it's great). I've heard good things about the C 110/2.8, but I haven't tried it. Based on the C 150 and C 210, I won't bother trying the C 300/5.6. Besides, it's getting a bit long to use T-S, and I already have the very nice Tamron SP 300/5.6 for 'straight up' shooting.
Here's some relevant links that you have probably seen, but what the heck.