[zoomzoomvaroom]

Wow this is a long tread with TONS of information and while I can appreciate it I have been overwhelmed. So please help dumb this down for me.
I have my original rims on my Z4MC and sadly the original tires from 2006. I am now up to 11k miles so plenty of tread for my old man driving style but time for new rubber. Car is summer only and I have decided on the MPSS (please no opinions on that, this is confusing enough). Now I just have two issue:
1) Size = Tire rack says 255/40ZR18 (95Y) XL on the rear and 225/45ZR18 95Y XL on the front. I see a lot of posts with lots of other sizes. I assume that to maintain the stock look that is the size I should go with but what tire size would you recommend? (not racing, just thinking of resale-looks-and driving feel)
2) Price = Once I know the sizes I can shop the internet with the best of you so let's skip the "try a google search". If you have some specific direction on where you feel the best deals can be had please offer it.