I'm racing with a 5/8" front. For street use, that's about as much as you'd need.
As Peter says, make sure your A-arms are drilled. If not, be careful, since these A-arms can be crack-prone if drilled improperly.
Agree with Peter on rear bar too. I got one free onetime and put it on for a practice session at Pocono. I pulled in early and disconnected it. A waste of time for these cars.