It depends on what your power goals are. You will make more power with high flowing heads than with stock heads.
By playing with a little 8th grade math, you can approximate the increase.
Lets say that you take the stock 225 HP 5.0 EFI and put explorer heads and intake and get 255 HP: that's a 12% increase.
Stock HP ÷ New HP = Total HP increase in %
225HP ÷ 252 = 12% Total HP increase
300 HP supercharged x112% (explorer heads and intake) = 336HP
These numbers are approximations, the real life numbers may vary widely. I would expect a little higher figure more in the 350HP range because of the increased flow capacity of the heads.
Yes better heads will make more power, but stock gt40s will make plenty to push block to its limits.
I have a 302 stock block, stock crank, forged rod and piston, stock gt40 heads, intake, throttle body, etc. Anderson n41 cam with on3 turbo kit. On 10 psi I made 520 rwhp. On 13 psi, we didn't make a full pull on dyno, but made a pull to 4800 and would have made approximately 600-620 rwhp..
So, yes, itll make more power with better heads and intake, which will let you run less boost for same power, but it is definitely not needed
So, better