Mixing tire tread???

I need to get new rear tires for my stock rims before attending a tracking event. My fronts are in perfect condition and are still the stock tires. I wanted to get the S-03 for the rears but was curious if it wasn;t a good idea to have a different tire tread from front to back? Not really sure why this would be a problem but thought I'd ask.

Also where can I get the best price for these tires at this time???

No one can give me any feedbacK, What gives

I think that for wet conditions sometimes it matters but it depends on the tires. I am currently running two sumi's in rear and two dunlops in front. I have no problems. This W&T forum takes forever to get an answer on. I think that the only times you really run into problems is when you mismatch tires on each side front or rear. For example if you were running one directional tread tire on your front driver and a continental all season on the front passenger that is where you might run into trouble but if you have matching tires on both sides just different ones in front and rear then you are fine.

Thanks! Thats pretty much what I was thinking, just wanted some one to back me up on my thought process!