I have made few posts on differences between XC 3401 VRG and BO6040. They can be found on MOL archive and on DU. There was also a good post on same subject on Autopia recently.
Cliff's notes: BO6040 has number of disadvantages biggest one being that it is very user unfriendly (hard to control) when used in forced orbit mode when compared to Flex.
Let me put it this way: Recently I met briefly with two high level pros with many many years of experience. I brought my XC and my BO6040 with me. They were not aware of my thoughts on Makita. Both tried out BO6040 and within minutes concluded they don't like it, put it away, and spent rest of the time polishing with Flex. In other words: Specs are just part of the story when it comes to tools. Other part, that can be argued of playing even bigger role if specs are close enough, is how easy it is to use. BO6040 would have to run circles around XC, or XC would have to be significantly less able to correct paint than it is, for me to accept what I find as flaws of BO6040 and live with them. From my experience with forced orbit tools (and I have tried them all) nothing comes even close to XC 3401 VRG.