i just dug out my BMW spec book and if my calculations are correct the wheels and tyres that will run best for looks on that E36 would be an offset of 28.20mm and a size of 215/40/17 and dropped on shorter and stiffer springs by 15mm to keep the spec as closest to the original performance.
if i was going for speed and racing i would go for a size of 225/50/15 with an offset of 41.20mm using a set of 20mm spaces to keep the offset in check.
then again lower it but i would need to drive it to get it how i liked it and felt it was best for my style of racing before saying what id lower it to.
so now the reason why it will slow you down because most people just chuck any old wheels on there cars without looking at the original spec they will always loose the diameter of the original wheels, the car isn't made to take bigger or smaller, so therefore it will effect performance all over the bigger the wheel the more weight u add to the car some wheels can add 20lbs per wheel so adding more weight will always slow you down? and the bigger the wheel means the Rpm will have to be higher to move the car off the line then over all it wont make a difference. on a BMW as their performance is in the Higher RPM. so it will be sluggish off the start but as it get moving it will then be easier on the car but not always benifitial. (sp)
after adding bigger wheels to a car you should always upgrade ur brakes if not change the pads and discs, and check them regularly
as said before i don't want to go into a willy waving competition of who thinks they are right and wrong and who know better then the others, so before we spamm the fook out of the thread so letts take it to Pm or i cant be bothered
could have fitted the DOHC into his capri as well. nevermind!
my capri may have tiny wheels, but at least its low! comes to the same height as an old mini 
wanna swap for 25 year old capri lights? haha!
the cast one on the car is about as efficient as paper shoes in a puddle