I consider 20's a perfect size for ur ride.
I have 19's but its because a low price was offered.
Also it depends on the tire height.
My wheel size is: 255/40/R19
Take I look, I posted the pics last week:
Down here at P.R. when buying a 19 inch tire for any 19's rims...well, lets say is not cheap.
19's can become more expensive than 20's when you do the math. It all depends.
But overall, I recommend some 20's.
Hope my opinion helped in something !