You must realize these following things:
-Ride height has nothing to do with handling in BMWs
-Springs have BARELY anything to do with handling in BMWs
-ebay cheap china sh1t will make your car ride like a 1988 camry
-BMWs arent vdubs and if you want to slam your car and put 11" rims with 205 tires then you got the wrong car
But if you really wish to improve the handling of your old BMW then you need to look into a set of new shocks, as thats whats gonna improve the handling.