Depends on what you want from the car - meaning what you personally get from it. Is it rarity? Performance? Fun to drive? Fun to cruise? Lays down elevenses when you mash the gas? Ultimately, what do you want from a car? Once you know that, then you can decide if the 911 or Cobra fits the bill. It's hard for us to tell you one way or the other if you are crazy or not - some might say yes, others say no. Others yet will say "meh."
I would love a late 70's to early 80's 911. I also don't own one. Meaning: it's easy to want what I don't have. While the car is certainly iconic, it will take quite a bit of coin to get the performance up, no doubt. A Cobra will have that in spades. So without knowing you, without really knowing the situation, I'll take a stab at a pros/cons list.
911 Pros:
- pretty damn rare, certainly won't see many of them
- iconic car, it's a Porsche 911 after all
- great handling out of the box
- feels like a sports car
- good curb weight, about 2800 lbs (resulting in weight/hp ratio of about 15.55:1 - which is just okay)
911 Cons:
- it's old, so stuff will break if it hasn't already
- it's old, made with old tech, and probably pales to today's performance; in other words, lackluster performance by today's standards
- it's expensive, it's a Porsche 911 after all
- you will feel like it is lacking in acceleration
Termi Cobra Pro's:
- it's supercharged, and has almost 2.5 times the power of the 911 (it's officially rated at 390 bhp, but it's really closer to about 430 bhp)
- still holds its own by today's performance standard
- blower whine
- it's a Mustang, so oem parts are more readily available
- aftermarket parts are plentiful and affordable
- you will not feel like it's lacking in acceleration
- good handling out of the box (perhaps not as good as the 911, but unless you track them you probably won't notice)
- feels like a sports car
- 6-speed trans and new(er) tech
Termi Cobra Cons:
- it's old, so stuff will break or is about to break
- it's a Mustang, which means there are like billions out there. Not like a termi, but only Mustang people will know that; everyone else will see a Mustang
- not as unique/iconic as a 911, won't turn as many heads
- it's a very specific Mustang, so depending on what parts you need, they might be harder to come by than a normal Mustang (but still easier than a 911)
- heavier curb weight, about 3600 lbs (however, due to the crap-ton of power, the resulting weight/hp ratio is about 8.37:1 - which is really, really good)
So really, it comes down to: what do you want from the car? Both cars offer completely different driving experiences.
