The engine is basically the same. The S320 has a 5-speed AT. From 95-99 the S320 was available in SWB and LWB (like the S420, S500 and S600). From 92-94 only in SWB. The S class is bigger but also more complex with systems like door and trunk lid closing assist. Test drive the more expensive S320s available so you have an idea of what they're like when they're at their best. Then look at the ones that are in the same price range as a 95 E320. See what works and doesn't work.

Sixto
93 300SD