It's not the top end that lacks oil,it's the cam lobes and lifter wheels that don't get enough oil. As BigSky and Burla stated your best option is a tuner and then up the idle rpm to roughly 750 rpm,and don't be scared to drive it a bit aggressively at times.
There's no pressurized oil fed to the cam lobes and lifter wheel,so pumping more oil through the system,isn't really the cure all.The cam lobes are still lubricated by the oil flung off the crank,so a higher idle rpm throws more oil onto the lobes when the engine is idling,and slightly aggressive driving that keeps the rpms up above 2500 rpm also throws more oil onto the lobes.
With the idle rpm set to 750,you'll have just as much oil pressure as the hellcat pump creates at 560/600 rpm,with the benefit of more oil coming off the crank to lube the cam.If you're hung up on the Hellcat pump,install your original bypass spring from your stock pump,and if you decide to go with the Melling HV pump,use the low pressure bypass spring,but you'll still want to up your idle rpm to 750