The 900 in 940 trim, is fundamentally the same car as the 740, with little improvements along the way. That's a broad brush stroke, but you get the picture. Similarly, the 940 Turbo is very similar to the 740 Turbo.

If you poke around eBay motors, you'll get a good idea of what the little cosmetic differences. There are many little details (this trim changed here, this bumper was body colored there) but not that much.

The 960 is a different animal. It can be reliable, but it can be a bigger mouth to feed also. It is very different from the 940 model line, mechanically. Also trim level wise. See posts by General Patton and Tom Irwin about Christine, his 960. It might have simply been cursed, but the 960/S90/V90 is a more complex car.

There is a "broad" description.
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chris herbst, near chicago