It's good to know about the evaporator. To get it replaced by an independent mechanic, think at least $1200. You could also do it yourself for far far less, but plan on a full two days of work to get it all done.

If you've done the belt yourself on the red blocks, just add 50% more time to the job and you have the 850. It's tighter in there due to the transverse mount, so you have to remove a few more things, but the basic job isn't bad. It is, of course, important to pay much more attention to tooth alignment. Misalignment on a red block means it won't start, or will run poorly. Misalignment on a white block means destroyed valves and piston heads.

As for DIYers doing suspension components, I've never felt like they were bad, on the FWD or RWD Volvos. I've occasionally had to bring a control arm to a shop to have a stubborn bushing impacted out, but other then that, if you're moderately experienced, most jobs are totally doable.

The 940 you mentioned also sounds pretty good. A couple things to think about. I know your experience with the 7 series lets you feel more comfortable with these cars, but I wouldn't hesitate to trust my life with my old 850, and newer V70 at least as much as my old 240. In many ways, the FWD are safer, and at the very least, when you're behind the wheel, they feel just as heavy and tank like as any red block. Despite my fears when I converted, they still do feel very much like the same old "Volvo" I learned to trust and love.

That said, your mechanical experience with the 7 series will definitely be an asset with the 9 series, they essentially have the same drive train. I've definitely had a learning curve familiarizing myself with the new layout of the FWD, but it hasn't been horrible.

In terms of choosing between the 940 or 850, I'm going to pretty much stick to my guns on the service record and owner history theme. While I think the FWD have much more to offer in terms of drive performance and ride quality and comfort, I would probably take a really great 940 over an "ok" 850. It will just be up to you to decide how much better the 940 is than the 850. I'd highly suggest driving at least one 850 before sticking with the red blocks. You may find you like the differences enough to either go with the 850, or find another better one. On the other hand, you may find you don't like the FWD changes at all, and sticking with the red block will be easy. Mechanically I think its probably almost a wash. The red blocks may have a slight edge on overall reliability, but I believe both engines are capable of extremely high mileage, and when taken care of, both are excellent cars.

Hope that helps!