Wheel deciding question ?

i have VMR CSL wheels that are 19" (for sale btw) on my 2004 e46 M3. I found a set of 18" wheels that i like but i didnt know how big of a difference it'd make. If you have any pics of your 18" wheels please post them or any comments or reasons to not make this decision. will this effect my driving/performance in anyway too? THANKS