What your asking is do the High Velocity Merge Collectors help. Yes they help scavanging a good bit, in a comparison we did on an engine dyno we saw a 5Hp gain across the board and 7 peak using a burns HVMC (no spike) versus a standard stamped 4 into 1. This was on a 10.0:1/CR 2.3L. As Mike said, primary length and size are the biggest part, but I believe that the way the header comes off the head plays an important role too. Its just a theory of mine, one day I'll be able to test it on the flow bench. Like your second picture posted, that comes off the head very nicely. You dont want to just go 90 degrees out the head. The larger primaries are required once you start moving more air like going up in displacement.