My E90 felt light, floaty, whatever at the top of the backstretch at VIR. All cars are going to be 'light' here but I did feel it wanting to wander around a bit. This was when I had the OEM shocks with Dinan springs. I was running EDC in the Normal setting. When I switched it to the firm setting the car felt more planted. That is why I recommended to OP try that.
Now with my KW coilovers it feels planted all the time.
Current: 2015 F80 M3 (SS, Full Black Interior, 6MT, LED Lights, Adaptive Suspension, 19's)
Previous: 2013 E92 M3, 2013 F10 M5, 2009 E90 M3, 1998 E36 M3