Need help on set of 4 tires for 2006/07 X3

[blaCkwinD]

I am having abit of dilemma with wheels before, so now i found a dealer who can supplies me 4 set at reasonably priced.

My Front tires shown: 235-50-18
Rear tires shown: 255-45-18

The dealer first said i can use the 255-45 for all 4, he only stock the 255-45-18 YOKOHAMA S.DRIVE TYRES but there is no 235-45-18 unless special order. otherwise i can have this instead 245-45-18 YOKOHAMA ADVAN SPORT V103 96W TYRES...

Now you can see one set is S.drive and other is Avan. As i believe x3 is sensible to different thread and type of tires.

Please advise would be appreciated.
Link is picture of what exactly look like my car

http://4.bp.blogspot.com/-Owx875ECe_...25281%2529.jpg

Thanks