I don't have the answer but my suspicion is that Dinan would be best. There are a couple of people on this forum who are experienced on the track and have recently installed Dinan springs. I am hoping to hear their impressions. I really worry about making the car worse with lowering springs. I have a friend that put H&R springs on his 335 and it was bouncy at speed and he regretted it. I'm also concerned with the issue of having problems with the EDC while having lowering spings on as these units cost a fortune. At least with coilovers you are not going to damage the stock suspension because it is replaced. With the cost of installation and alignment I want to let the issue play itself out before I make a decision.
2015 f80 M3, 2010 GR3RS