"coilovers" don't make a car understeer, the setup does. Variables are:- Sprint Rates, Front/Rear Rate Ratio, Bump and Rebound settings, Caster, Camber, Bump Steer, Corner Weights, Ride hieght, the Rake of the car, etc. All a coilover is is a strut which is adjustable.
If you find yours to hard, buy some softer springs, knock the damping down a bit and in most cases, if the rest are setup right it will be no slower on a public road.
If you only want them so the car 'sits right' then find the cheapest you can.
All IMHO of course ---john---