700 / 900 series are RWD, essentially the same car but 700 series discontinued prior to 1994. The 960 has a 6cyl engine; also available a 940 turbo w 4cyl engine. In addition, there's a 940 (4cyl) normally aspirated, but it's underpowered. I owned a 94 turbo 4 wagon and it was a totally reliable car.

The 850 is FWD, and somewhat smaller, and 1994 was the second year of US production. Nifty 5cyl engine (a Porsche design).

General consensus on this board is that the 900's would be considered more reliable, the 850 less so (but more sporty, though a somewhat stiffer ride). Both are comfortable cars with great seats and ergonomics. The RWD and FWD systems each have their advantages.
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David (98 S70 T5SE Black, misc mods (mostly lighting), red calipers) (92 940GLE)