the e320 was 4matic. that slows it down a bit. I have a e280 and it does 8.1 measured with a racebox. 7.8 doesn't sound that far fetched in perfect conditions
Actually mercedes fitted a very short ratio differential for the E200. That's to make it accelerate faster. Notice when u move up the range such as the E320 or even the E420/E430, acceleration times doesn't seem impressive but u get very low cruising rpm and a pretty good top speed.