Tire size and performance question

[conester2013]

So I am mini tubbing my 69 Camaro this winter and I am planning on going with 275/35/18 front and 335/30/18 in back. Can anyone tell me if this is a good set up for Autocrossing? Some say that a big difference in size from back to front isn't good and others say its ok. Would 315/30/18 be better out back since the biggest I can go up front is 275, or does it matter? I could go with an 11.5" wide wheel and then use either size in back....

Thanks!

Brian