Ride height and spring rates are a bit of a science,if you reckon you can get it right the first time or even the second time go for the fixed units.If you need more attempts to be 100% happy then the costs of a full coil over set up will start to come into play,as for track work,if you start to get serious you will potentially have a differant set up for each track.eg. there is no way you would use the same set up at Q.R. as at Pittsworth Sprints(too bumpy)if you did"nt have to.As with bikes the CG is the base point for handling on any thing with four wheels,get this as low as possible without changing base geometry and everything else will follow.It"s all a compromise with production based vehicles and in most cases with the size of your cheque book,give yourself some thinking time to fully address all the issues.Cheers