Wheel Offset size suggestion

I own a 03' LS430 and need suggestion with offset on a WALD DUCHALET II 3 piece in 19's, and DUCHALET II Forged in 20's. Looking to run flush with the fenders, and running it with JIC FLT-A2 VIP Coilover.

Your expertise will be much appreciated.

Thanks.
Eric.

with shaved fender lip and moderately stretched tire
x9 +10
x10 +15

^^ Somewhere in the high to low teens should do it.  Just make sure you get high disk for the wheels upfront, to clear the big brakes.