Eibach tends to be very conservative with it's lowering kits. The basic reason is because you don't need your car dumped to turn. Lowering the car mildly, combined with firm suspension, will enable most any car to feel significantly more stable during handling manuevers. This is the aim of Eibach street application kits. Provide realistic lowering, while increasing handling dynamics, with as little sacrifice to ride quality and tire longevity as possible. Superior reputation and build quality are also a plus.
TurboKA37, performance in handling is not just a product of ride height and spring rate, as I'm sure you know....Both kits increase handling dynamics, one will lower the car more than the other.
Pro-Kit is the mild kit, giving least drop and best ride quality...while Sportline kits are what Eibach call extreme lowering. The public is clearly fascinated with lowest possible ride height...this may be while Sportline seems popular..