I owned a 2005 GTO with the LS2 engine for just under three years. I loved it. And it has a story like the Crossfire. German chassis (Opel) from the late 90's, US drivetrain (LS2 & Tremec T56), styled and assembled in Austrailia by GM's Holden brand, sold in the US as a Pointiack.

The engines are very similar in nature. The little AMG blown V6 has a broad flat torque peak just like the LS2 V8. Both engines run out of steam around 5,800 RPM. They don't breathe extremely well at high RPM and don't like to rev really high. But that's OK, they don't need to. The good news is that you can feel and hear when both engines are approaching red line. This is in stark contrast to my S2000 which would scream all the way to 8,200 RPM with no warning at all that you were approaching the rev limiter.

The transmission is where the two cars really begin to diverge. The Crossfire has a wonderfully slick n smooooth 5 speed automatic gearbox with full manual control. The GTO has a @$#%ing annoying Tremec T56 gear masher with an even more annoying CAGS "feature" built in. I think the T56 design is compromised by its very nature, a manual gearbox designed to handle more than 400 lb/ft of torque. At any rate, shift lever throws are long, shift gates are clunky, and the CAGS system is the dumbest thing ever done to a transmission. After 6 months with the T56, I regretted passing up GM's really excellent 4L65E 4 speed automatic. The 3rd gear gate was especially problematic. A 4-3 downshift was always a 50/50 proposition. The T56 does not like to be rushed. You need to plan ahead and slow down your shift lever movement or the thing will balk at gear engagement. The T56 is by far the worst manual transmission I have ever driven outside of a truck. The clutch was fine though. Not too much effort given the torque it was managing.

The two Chassis both have stories as well. The SRT6 started life as a Mercedes roadster with reasonable stiffness to which Chrysler added a fixed roof for even more stiffness. The GTO started life as an Opel sedan which GM's Holden group cut down into a coupe body there by increasing its stiffness as well. But, where the end result in the Crossfire weighs 3,200 lbs, the GTO ends up clearly in the grand touring class at 3,700 lbs. That weight difference make a huge difference in driving enjoyment for me. Neither car has top notch steering feel. Both steering systems are geared on the slow side and neither one has really excellent feel. But both are very livable after a month or so acclimating to them. On the plus side, the Crossfire's 32.4 ft turn radius makes it way more maneuverable in tight spaces than the GTO's 36.1 ft turn radius.

The GTO obviously adds two rear seats. They are a PITB to climb into but once seated, they are really roomy and comfy. GM should have used spring loaded mechanical seat rails on this coupe rather than the painfully slow electric motors. The SRT6 wins on useful trunk space as the GTO has the gas tank mounted in such a way as to leave you with a small, oddly shaped place to put your cargo.

For its price point the GTO has a very decent but simple interior with a decent audio system that lacks many of today's standard features. Likewise the Crossfire audio system is a bit dated but functional. Both cars have nice seats and good instrumentation. I'd have to give the nod to the SRT6 for overall quality and design.

As for performance, GM claimed 4.7 0-60 for the GTO and Chrysler claimed "under 5 seconds" for the SRT6. Road & Track reported 4.8 seconds. I'd call it a tie for acceleration. As for braking, it's no contest. Road & Track measured a 0-80 stop for the GTO at 221 ft whereas the SRT6 stopped 20 ft sooner at 201. That's not the whole story either. The SRT6 brakes have much better feel. The GTO brakes aren't horrible but they're trying to control another 500 lbs and the Goodrich KDWS OEM tires sucked.

As for fit, I'm very close to your size at 6'0" and 215 lbs. I find the Crossfire very comfortable and plenty roomy with good ergonomics. But then, I found my S2000 comfy and roomy enough. I think this one is purely subjective and it comes down to what you can tolerate. The Crossfire does have a chopped roof effect from a high belt line and very short windows along with a narrow rear view. I can see how some people might find it a little too claustrophobic.

My GTO would get 18 mpg in mixed driving and could reach 25 mpg in pure highway cruising. The Crossfire returns about 20 mpg in the really heavy traffic I commute in now. I have no idea what its capable of on the highway as I've never had it out for a long highway trip yet.

A final note on the Infiniti. My wife drives a 2008 G35x with the Nissan 3.5L VQHR engine. I LOVE the engine. It has a 7,500 RPM redline and loves to rev. It's one of the best NA engines I've ever experienced. But, its fuel economy sucks. Unfortunately, I haven't driven the Infiniti manual transmission so I can't give you any feedback there. The G35x returns about 18 mpg around town and the best I've ever seen on the highway is 24 mpg but 23 mpg is more typical.