Just as an aside, if you’re not aimed at the IBR or other rallies, there is no limit on fuel volume on board for cert rides. I noted that the size you want to stay under the 11.5 Gal rule is not nearly as common as smaller and larger aux tanks.
I was an FJR rider for much of my rally riding, then moved to the Super Tenere. As you said, still plenty of low mile Sport Touring bikes around at reasonable prices.