20vt s gonna be the fastest
non turbo means weak torque and thats what wins the the races
would be easier for u to convert your 8v to VR6 TBH, and wont cost you anything
to go 20VT properly is gonna cost you a fair bit.. i do have a engine for sale tho with all the bits you would need from the donor car (engine, loom, ECU, Gearbox etc etc)
I personally would not swap my current engine set up for any other in my mk3