I don't have a compressor map in front of me, so I can't comment on the turbos being outside their efficiency range.
Regardless, those turbos are still pushing over 500 cfm each through a core that can efficiently support only about 125 cfm (@ 1 psi drop). There is big pressure drop...trust me. I wish they measured the pressure drop on these runs, although I imagine freezing the IC helped a lot in this area