The car is awesome on track with the solid engine mounts. It feels like the engine was lowered 2". In reality it just isn’t wiggling around as much. I could not perceive any difference with the solid transmission mount and the sport diff mount. This was a night and day difference.
I’d say it only really vibrates at low engine speed, especially in first gear around 5 MPH. But then it isn’t noticeably running rough: it never feels bad through your hands in the wheel.