Tell me, how many races are done with HP per Liter? Or how many are won?? HP:Liters is NOT a calculation you want to spew out to anyone who's serious about cars. Unless you're possibly talking to or about F1, NHRA or....dare I say....NASCAR. Or something of the like.
But onto the questions.
How does a car like the TibGT have 6 cylinders.... Stop. Cylinder count matters not in performance (it really affects the balance of the motor and power delivery more I would say). Displacement does. Yes, yes, it's a v6...but it's also a 2.7L v6. Ok, let's continue.
The Delta (engine in the GT) is very inefficient. It runs rich from the factory yet is choked off from air. That's just it's design. However...because of the fuel trims and timing maps, like you stated it takes to both N/A and F/I pretty well. Cold air intake, Headers, Exhaust, tune can get you over 30whp. When's the last time you saw that with a honda with the almighty VTEC or, i-VTEC, or whatever else they're putting in their engines...?? (to be serious, I really don't know if you can get 30whp from i/h/e/t with honda engines...if you can I'd love to see it).
With the tib, I'm sorry to say, you're more or less paying for the look. The stock clutch is terrible, the flywheel is heavy as hell, the paint is more or less crappy, but, you get the look. For some, that's all that matters.