I currently ride a 60cm road frame with a 58cm top tube being just under 6ft 3", do you go with the same size or something a little smaller
Personal preference really in my opinion.
I went slightly smaller and as light as I could afford. Just remember, If you are doing proper cross courses, you will be slinging it over your shoulder to run up some parts. So you don't want any bottle cages getting in the way either.
Also, again in my opinion, you want the simplest mech's and shifters. Something thats easy to clean, take to bits and put together again. My crosser came with 105. All I kept was the crank and switched everything else to my road bike and got 2300 shifters and mechs with an 8 speed on the back. Keep it simple and light, slightly smaller than your road bike as you'll be on and off it alot