Can you put 245/35 front and 295/30 back? 
Or do you have to go with 265/35 and 305/30, which seems to be the more popular setup? 

Is it a safety issue?  Weight of the car being so heavy.
Maximum weight the smaller tires(245/35 and 295/30) can handle is 1565lb front and 1874lb back.  Maximum weight for the larger (265/35, 305/30) are 1819lbs front 1984lbs back.
Or is it a performance issue?

BMW alpina comes stock with 245/35 and 295/30.  And the specs are similar to PanTurbo.