How much easier is College Board SAT II Bio M than Barron's one?

I had been looking for a 750+ score on the college board SAT II, but I’ve been scoring 670-ish in Barron’s, so I don’t know if that’s realistic anymore. Would anyone mind giving me a rough estimation of how that would convert?

Bio is a tough subject test, IMHO. Csi darned much possible material. You can’t tell until you really take the test.