3 bar heads are GT40 heads, while 4 bars are GT40P heads. Both are great heads when ported, but I can't offer any data on which is better than the other. I do know you'll have to buy a set of GT40P specific headers, if you go with the p's. The spark plug holes on those heads are perpendicular to the block, rather than at an angle, which is why stock and most aftermarket headers won't work with them.
66 Coupe- 5.0 EFI, T5, 8.8, 4-wheel-discs, blahblahblah
Carolina Crew #82