The guys here are leading you in the right track. For most XC racing, 46-48" wide is usually ideal with 22-23" front tires and 22" rear tires. With that said, Setups all depend on the type of trails your actually going to be running. Some XC racing is done on courses that also accomodate to UTVs while others were originally designed for dirtbikes.
Here's a video of my brother and I on what is a typical trail in central NY. Both Honda 700s in the video are 48" wide and on 22" tires all the way around. If you plan on racing in tighter areas, I'd stick to around 46-47"