The 560 had the more reliable engine, along with more power and torque. Gas mileage will not be great. Things to look for are rust, operation of all the luxury goodies, and rust, especially in the northeast. Condition is more important than specific model year or mileage. Also, timing chains and guides are a wear items on the V8's. The overall engine can last about as long as a similar era diesel, but will go through chains and chain guides which should be replaced every so often. I don't remember the exact interval but I think it was in the area of 130,000 miles.

__________________
Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 401,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 26,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.
99 Mazda Miata 183,xxx miles.