The subframe on the XR650R is one of the biggest weaknesses when being considered by dualsport riders. Having a lot of weight far back on the bike will eventually cause the subframe to break. There are a variety of upgrades which can be done to improve the strength of the subframe. One of those upgrades is increasing the size of the mounting bolts from 8mm to 10mm.
The stock subframe mounting bolts are 8mm with a 1.25 thread pitch. You can drill these out to 10mm and tap them. The mounting points will be significantly strong and the bolts will be less likely to become over stressed when carrying a load.
It’s not an end-all fix – it’s just one step in strengthening the rear of the bike. There is more information about this topic on the site.