I guess it depends on what speed, and when the torque curve drops off on the engine. I know a NA OM603 engine has a torque curve that diminishes after 2400 rpms, and a turbo 603 is just in the initial stages of it's upper rpm "thrust".

If the E300(OM606) is at all similar to the old non-turbos, then it is the weaker car on the highway by a large margin(despite the hp). The 2.5 turbo should be in it's prime on the highway.