TXGS507

So, I recently purchased some Weld RTS wheels for my built C5Z... I went with the C6Z offsets and they fit perfectly... Was originally going to use them only for 1/2, 1 mi events but the looked so good I am going to order the fronts. My C5Z has the wide body kit in the rear, w Eradispeed2 pc rotors... they are 18x11 w MT 345/35/18...

I wanna pick up the fronts this week as there is a waiting list.
I want to run an 18x9 ( high pad) in the C6 offset as I am also running a 2pc 13.35 rotor up front... Was wondering if 6.1 backspace will be enough... will be running a 275/35/18 tire up front... Just sold my F14's w the C6 offset ( 18x9) w the same tire... I do NOT know the back space..? Weld recommended the C6 offset w 6.1 backspace in an 18x9... any of your experience, input would be much appreciated... Here are the rears...

Thanks in advance....