I don't think we can draw a direct correlation between the prayer of John 17 and the intercession that Christ does in a high priestly role. For example, Christ prays for the disciples, which includes Judas, and clearly Judas is not elect. Christ says he prays them, and that he has not lost one of them except the son of perdition. Interesting. That doesn't make any sense to me. I don't know how they get around the idea that everyone in the New Covenant is regenerated. If you don't mind, I'd be interested in know which RBs argue this. I'm not going to push that argument because forming doctrine from typologies is always tenuous, but I think the argument can be made. Obviously Christ's sacrifice is better than the OC sacrifices because it actually does (or can, to a 4-pointer) remove sin. I don't think that Jesus becomes a person's high priest until he intercedes for him, and he doesn't intercede for someone until they have faith.