^ hater, lol.... but seriously, some questions I don't know the answer to:
1. doesn't the G37 use the same ATTESA AWD system the GT-R uses, or is it diluted?
The new GTR uses a totally different type of AWD system. They're both called ATTESSA-ETS, but the similarities end in name and their ability to go from 0:100 to 50:50. The G37 uses an electronically controlled clutch to bias the torque front to rear. Other than that, its open differentials in the front and rear axles and uses the brakes to bias torque left to right. With an open diff, if you apply brake pressure on the left side, more of the power goes out the right. If you fully lock the left, it'll go 100% to the right. It works on street vehicles, but its reactionary, and chews the hell out of the brakes. The other upside is open diffs weigh less than other options.
With the GTR, the transaxle includes both the transmission and rear drive. It uses a 1.5 way mechanical LSD in the rear and open diff in the front. It has more advanced yaw sensors and stability control than what the ATTESSA-ETS in the G uses, and its tuned for aggressive driving to let the back end slip out a bit.
and 2. using your line of logic, doesn't that mean that the S5 could be faster if they didn't offer it in an Quattro version? or are you saying that the quattro version is implemented in a way that the extra weight is overshadowed by improved performance?
If it wasn't offered in a quattro version, it'd be FWD, like all other Audi's. So its AWD or bust.

My main point is that the G37 with the 6 speed is only 60 lbs lighter than the A5 with Quattro. G37 with the automatic and AWD would be pushing 3850-3900 lbs, since AWD is always 200 lbs extra and Infiniti has never offered a 6MT with AWD. So with that extra weight, some of the advantage the G37 has with the engine, is eaten up with that weight. You can null that out if you get the A5 with automatic, but we're getting further and further away from sports coupes at that point.
Wasn't comparing the S5 to the G37, too much of a price and performance difference. But comparing G37x
S coupe to an A5 with the S-Line package, I'm going A5 before G37 even though its still a couple thousand more. It'd be a hair slower, but neither is very fast, has better lines and I think there's a good chance it'd handle better.