i have an 04 g35 coupe with tein s-tech springs riding on OEM 18's

I plan on upgrading to volk gt-c's in either 19's or 20's not sure yet... right now i have about a 2 finger gap in front and a 1 finger gap in back. If i were to get 19's or 20's would it fill those gaps up? I sort of want the tire to tuck a lil bit but not too much... i am very confused on what size tires, rims i should get in order to achieve this... i'm afraid if i go with 19/20's that the gap will still remain the same... so do i need to get 35 series tires for the front and 30 for the back, or 30 all around? what do you guys recommend?

 

on stech's, there will be gap with 19's @ 35's ff and 35's rr. with 20's, there will be a smaller gap with 35's front, and 30's rear.