If you are happy with the A/F ratio at low engine speed under load 2000-3000rpm, I would leave the PVCRs alone.
For some reason, there is a few complaints of lean "out of the box" Ultra XP 850s.
Here is one thread on the subject:
new holley 850 ultra hp WAY out of wack - Yellow Bullet Forums
So I'd start experimenting with the high speed bleeds.
Gary