Yeah.. MMR made one key mistake, adapter plates. Even the inventor of the plates is up front about them wrecking the air flow path, moving the injector to a crappy spot and consequently driving up the BSFC. If they'd take the time to grab a HPS intake and port it or even fab up a sheet metal intake they'd see a definite power gain. They have a deal with edelbrock to pimp that intake and with Professional(ly shitty)Products to pimp off their adapter plates. I was involved with the development of PP's plates and they're ok but they're not good for power at all. They cost me 10hp at least, dyno proven and that was with my shitty heads. With the TFS heads (especially ported) the difference would be more dramatic.
From the 2v, I just don't see 500rwhp NA happening on a streetable combo. 500bhp NA I can see no problem with well ported TFS heads and some custom cams.