curious what everyone is using for rim widths on certain tires. reason i ask is that i have 12.5 on 10s right now. and have beadlock kits for a set of wheels. knowing that i will add about an inch if rim width with thes installed. i am going with the iroks
39.5x13.5. should i use an 8" rim to install the beadlocks with these tires?

Yes. Start off with an 8" wheel.