head flow cfm and HP

[Paladin]

Multi-part question here guys. Got my mustang back from the Dyno, and a vacuum leak was costing some serious power. Anyway, you can see from the print power climbs nicely til about 5,600 then just flattens. The upper line is from a dyno run 3 years ago that made 477 rwhp at 6,000 rpm. Wondering if my springs are gone and causing valve float now??

Also, anyone have any loosely based calculations on head cfm to hp? For example, my current heads flow 215 intake 185 cfm exhaust at .51 (my max cam lift) The heads I want to switch to flow 250 intake and 215cfm exhaust. Based on the improved flow is there anyway to estimate hp/ torque increase? Complicated by the fact I am running 10 psi boost.

thanks