No they really are a 603 down a cylinder, so power is down a bit. They are not as smooth either because they are a 5 cylinder. MPG is much better though.
Not sure about 0-60 times, but a properly tuned SDL should be in the 10 second range.
If you want fast the 1987 300D's are about as quick as they get until the E300D's of 1998-99 vintage. Those with Supertuning's chip are down right fun to drive.
It all depends on what you want, you know what a W124 is like. The LWB W126 is better on the highway, but they hate around town work. Espeicaly the 300SDL's they do not like running around town one bit.