Hard to answer your question without a little more detail. What 75mm turbo is it, how hard are you pushing it, and on what fuel/intercooler?

But really unless the heads you have are damaged, usually adding boost makes a lot more sense, and is WAY cheaper to gain power then adding head flow.

My 3700lb pig went 10.08@136mph with a 75mm and home cleaned up iron heads. That was at 20psi of non-intercooled boost. I don't know how close you are to that kind of power level, but it shows you can do pretty good without much head flow.

I now have CNC ported eddy's, better intake, bigger cam, billet 76mm wheel, and 23psi of boost, and it's been 9.55@142mph. Now the thing is 2 full tenths of that was in 60ft. So it's really only about 3 tenths quicker and 6mph. Some of that HAS to be the added 3psi of boost too. So I can't say that the heads were really worth much of anything at all honestly.

Adding boost is usually around 20-25hp per PSI. My car went 123mph on 10psi, and then 136mph on 20psi with the exact same combo. That's about 20hp per PSI almost right on the money. As long as you're not knocking on the door of detonation with the fuel you're running, it'd be foolish not to just add 4-5psi for 100hp. I can almost guarantee you won't get that from cylinder heads.

People are afraid of boost numbers for some reason. It's really just a number. If the motor will take the power, and the fuel octane and/or intercooler keeps detonation in check... you can add a LOT of power basically by just turning the knob for free.