The vane pump itself is not the issue. 130ish lpm injectors, pushing 320cc on the bench, and I can maintain 150 plus psi with the ksb on at wot. And that is with a little less than 10 psi of inlet. Again though, I don't understand why "case pressure drop" is of such concern. ksb on a toggle, and adjusting the regulator accordingly and you'll have all the timing advance needed.
The issue with case pressure drop is the regulator. However, inlet pressure also helps.