Tom,
I've been using C/V Bessas for the last couple of years. I have L, T, R2 (non-A), and R3A bodies. I've used the 15, 21, and 75mm lenses. Of the cameras you've mentioned that I know, I'd put the build quality on the T, R2, and R3A in the same range as the Pentax MX. I haven't used an OM-2n, and it's been over 20 years since I sold FM2's, and I never used them. It's not Leica M or R build quality, but I don't find that the cameras feel flimsy or are unreliable. I hear the R is not as rugged, and the L is certainly not as well built as the T, R2, or R3A. The only quirk I've found is with the film transport. If you tweak or spin the sprocketed spindle to the right of the shutter when loading film, the advance sometimes sticks. You can just gently rock the spindle and you'll feel a little click when it frees up again. This doesn't happen every time, but it's not exactly rare, and I've never had a problem with it staying stuck.
One of my four bodies, a T, came with a vertical RF misalignment, relatively minor, but it bothers me just a little. My R3A was banged on the baseplate by a loose monopod when I swung to avoid getting hit at a soccer game. That knocked the vertical RF alignment out a little. I was able to quickly reset it through a hole under the hot shoe and it's been fine since, even in critical circumstances. It took another hard hit from a soccer ball shot (right on the lens shade of the 75mm) 3 weeks ago and is still fine for RF alignment.
I haven't used the 15 a lot, but it's a fine, sharp, contrasty lens with the fall-off and special perspective you'd expect. The 21 is very nice as well, very good contrast and resolution without a lot of fall-off. The 75 is now my most-used lens, as it allows me to "edit" in camera in a way I like. It's very sharp and has very good contrast. It does a great job with Efke 25 and Rodinal 1+100 and with Velvia. I've noticed a little loss of contrast at the center when shooting backlit, with the sun just out of frame above the shot, but haven't seen a lot of flare. I've shot it a lot wide open at f:2.5 for indoor soccer with good results, and I get round, pinpoint stars to within a few mm of the edges doing guided astrophotography wide open with both print and slide film. Seeing those results for the first time wowed me. FWIW, Erwin Puts says it's a derivative of a famous 75mm f:2.5 Elcan (E. Leitz Canada) lens. I just go by my results.
For shots with the 75 see:
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and
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You can easily see the individual threads in the car bra stitching on the first shot, and you can count threads in the fine vent mesh in the shadows to the lower right.
Word is that the 35mm f:2.5 Classic is also a great lens, but I have a couple of 40mm Summicron-Cs, so that's not a priority for me. The 40 Nokton gets mixed reviews, especially on bokeh, but it's very sharp and faster if you need that. The bokeh sample shots I've seen haven't convinced me that it's bad in that regard. Lens build quality is not as rugged as Leica M or R, but it's very good, and all metal, even the lens hoods. As I said, the 75mm took a direct frontal hit with a hard soccer shot with no problem.
I now do a large percentage of my shooting with the R3A and T bodies (you can still get new Ts from cameraquest.com for $185). I love the 1:1 finder on the R3A, but if you shoot 35 or wider, or if you wear glasses, it may not be for you. The R3A with a mini 28/35 combo finder would also get you a nice set frames while still being low profile. I wear very close-fitting glasses and can barely make out the 40mm frame on the R3A with my eye centered, using peripheral vision. Reports are that most glasses wearers can't see the 40mm frame on the R3A. The reason I like the 1:1 finder so much is that you can leave both eyes open and see nearly your whole field of vision normally, with a reference frame for your shot floating in front of you. It makes me feel like I'm still in the world instead of just observing it, and I can see the context of the shot and anything coming from or happening out of frame that might affect the shot. Great for sports and action. So in Afghanistan or other places where you want to shoot with both eyes open, it might work well for you.
Hope this helps. Let me know if you have other questions.
Lee