KW coilovers is something I would really want because the height can be adjusted anyway you like. Basically the car can be slammed all the way to the ground. Its possible to raise it up anytime you like or lower it anytime you like. If you got the money to buy this then this is the product for you!
H&R springs is what I went with. H&R springs will set you back about $300 while the K&W will set you back $2,500. Me not having that much money to play with i went with lowering springs instead of coilovers. H&R brand. It lowered the car about an inch in the rear and about two in the front. This product is the bang for the buck! I use it and i recommend it.
BG springs, cheaper then H&R springs but i havent heard of anybody using them on their e65 e66 BMW's, so i dont know about performance of the BG springs. Eiback springs, also cheaper then H&R. I know few people that used eiback springs. Good springs, about the only difference i know is that H&R lowers the car a little bit more thats why i know more people choose H&R springs. If you dont want your car lowered alot this is the product for you!
All these are awesome products, you decide what to buy based on how much $$$ is in your wallet.
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