1. Agree that it's not a CVO, that they're giving you a snow job, and that dealers/sellers try to trick-F us on both sides of the deal. And how much extra is the seller trying to get for having a 120R in the bike? Most want a lot more $$ for 120 vs 103, but is it worth the full amount they want? (see next few comments)
2. Ask SDCVO (and probably others on here) who had the 120R blow up on them. Sure, for the first 20K miles or so they were happy...
3. You asked about reliability, but reliability isn't in one or two long trips; it's in avoiding the side of the road with a blown engine out in BFE where you don't have cell service so you can't even call for a tow--and watching a week or more of your vacation go down the drain.
4. Note that several of the people who're happy with the 120R had lifters and other things changed to more reliable parts. Are you willing to put more coin in it to do those reliability upgrades? O/w, it's not really known to be that reliable. Along that line: neither is the 110, unless you change the lifters, springs, and probably the valve guides too. Depending on crank runout, may need oil pump and cam plate as well.