285 xtreme comp cam?

What rpm are you trapping at? Have you tried lowering shift points? I'd expect what you have to peak much lower than 6300 and you may be losing some ET/MPH there.
In my opinion - the 284H will not give you much more over what you have. You might try going to a solid flat tappet instead of hydraulic. Something that give more area under the curve without raising the cuve too much... Torque rather than horsepower. Something like the XS274S or 282S if you really want "more". Look for another 4-5 degrees @ .050 and anothr .030-.050 lift. With what you have you're only getting about .460 lift at the valve which leaves a bit of those heads' abilities on the table.