As you probably know, the 850 and 70 series have front wheel drive and are fairly similar with the latter featuring a more compliant suspension and cosmetic updates to the front and rear clip and interior. The light turbo motor became available in 850's (GLT) in 1997 and continued with the 70 series GLT models. With the intro of the 70 series in 1997 for the 1998 model year, two all wheel drive wagons became available in the States.
The 900 series is really an updating of the 700 series which was introduced in the early 80's. It has rear wheel drive and features a very similar running gear to your 240.
The handling differences between FWD and RWD aside, the 850 is around 10 years newer from a technological standpoint. The 700/900 series are desirable because they are reportedly easier to work on and are not as complicated. The automatic transmissions are believed to be bullet-proof, not something that can be said about the 850. The 850/70 series are desirable because they are newer and some feel handle better.
It really comes down to personal preference and pocketbook. Good luck.
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