The W124 300E sedan and estate/wagon have the same track and wheelbase. Of course, the wagon is heavier, and it does have the self-levelling suspension. However, the 500E also has the self-levelling suspension, so you should be able to make the wagon handle as well as the 500E with the proper upgrades.

A W124 300E and especially the W124 SportLine, handle much better IMHO than the 500E due to the reduction in weight (both unsprung and static).

Hope this helps,

:-) neil