3 angle 'valve jobs' have been in use for decades in race cars. When used with porting it does help, but you can over do it. In order for it to be optimum, all components need to be matched. Intake flow, piston head design, valve seats, exhaust port, exhaust, camshaft lobe lift and duration. All of this is performance race car stuff.
Check with Allan Barrett on all of this!
Tom