The 300E up to 92 had the 177HP/188lb-ft torque M103 engine. 93 and later 300E's had the DOHC 3.2 I6. The 300CE had the 177hp/188lb-ft M103 until the 90 model year. During the 90 model year the CE got the 3.0 DOHC engine making 217hp/195lb-ft. Then in 93 the CE and 300E both got the 3.2 DOHC engine making 217HP/229lb-ft of torque.
The 400E is NOT the same as a six but "with a V8". Chassis and driveline mods/fortifications abound, biggest brakes you can fit inside a 15" wheel with 4 piston front calipers, beefed tranny, HD suspension, most 6-cyl options standard, and the aforementioned V8. **See MercedesShop reviews** The 400E may look the same to the untrained eye, but blow off some Mustang (or similar vehicle) and you will really appreciate the difference. Handling feel between the 6's and 8's is different. Both are very capable handlers (especially given better rubber and/or tires) but the 6's have a more nimble and tossable feel. The 8's, although more capable by the numbers, have a heavier "feel" to them. I can personally testify that 400E's make wonderful daily drivers as well as one of THE best performance sleepers. (only that 1" 4 where the 3 usually is gives onlookers a clue that there is 275+ HP and 300lb-ft lurking underhood vs the 177HP/188lb-ft of your average grocery getter) Then there is the 500E but that nudges into "4-door Porsche" or supercar territory...EG
Hope this helps....Lee