Guys.. trust me.. this is one of the best coilovers out there in the BMW community for the track. You can also pick any spring rate you want. It's also streetable as well.
A lot of E46 M3 track junkie guys that I know on m3forum.net have TC Kline coilovers.
Even though HP Autowerks is a competitor vendor with me I put a lot of faith into the TC Kline product.