Personally, I would take a VG over just about any toyota engine (aside from the diesels) Now as far as saying which is better, well that's just a matter of money. As far as the plenums being a restriction, yes they are huge issue that is VERY overlooked on the VG's thankfully custom plenums are a bit easier to fab up then a set of custom heads and would probably net a good amount of extra power as well as increase intake velocity compared to any stock lower plenum. But we are not here to get into a urinating competition about something as frivolous as who has the better motor, we are here to compare an 87 supra to a z31. (although I really think choosing the 84 to compare is a bad choice) I would say with some minor mods the z would actually hold itself together pretty good, but there is no comparing a modified car against a stock one..