FWIW I have similar spring rates to yours and when I was running both FM sway bars it was too oversteery for my taste. It wasn't absolutely horrible, but particularly in off camber corners I found the rear was just a little too eager to come around. It was manageable, but not exactly confidence inspiring in those blind downhill left-handers. The car feels more neutral with a stock rear bar. YMMV

I'm going to have to get out there and find the limits to see how it does I guess. I figured I might need to change bars so I was planning to bring the stock one to the track with me if I didn't get a chance to try the car out beforehand. There are few good places to try some things out other than the track.

UPDATE EDIT: Follow the progression here.