wheel help

I am about to buy some new rims for my s14 i'm thinkin 5 zigen copse but i'm hot sure what size to go with. I would like to go with 18's if possible but then I dont know what size tire to go with. I've heard from different sources that a 225/40/18 would be best but others say go with the 215/35/18. I dont want to sacrifice performance so which size would be better. Also do you think these wheels in hyperblack would look good on a white 240. Thanx for the help and any advice or recomendations would be appreciated.