Dave,
We are all enthusiasts here. I don't even own a Crossfire, well not yet at least. It seems you've done your homework and put together a very nice list of cars. I've got few things to say about each...

Xfire - Awesome car, Awesome Price! It's a rebadged Benz for half the money, I don't think you can lose. The handling is off the charts but is still lacking on power. If you are looking for a head turning luxury sports tourer this is it.

C6 - Pure American Muscle! You can't beat the Performance for Price. You pretty much get a vehicle that will run with just about anything for a fraction of the price. It also has a lot of technology and was very well engineered. My only complaint would be production #s. I have seen at least 1 or 2 C6s every day for the past few months. That's more 300s than I see in a week, let alone Xfires or Jags. I can't drive a car that everyone else has, I don't know why but I can't. Plus, I know the price is getting up there on the new vettes. If you can afford it and don't mind having the same car as 2 or 3 other people in your neighborhood alone then this is it!

'05 Stang GT - I absolutely love the styling. But, same story as the vette. Every kid at my old high school will probably have a V6 pony in a few months. I feel you hit the nail on the head with the word "juvenile." All in all, its a great car that is begging to be modded. It is already fast and with a few bucks can be even faster (almost vette fast from what I have read). Another issue I have is the interior styling, its not to my liking but maybe that's just me. To sum it up, Awesome looks, Neck Breaking performance, Mod Ready and you get the envy of every teenager across the country.

Used Jag - I don't feel comfortable comparing this to these other cars. It is in a class of its own. Also, it is used and used cars *could* have problems. Fixing a Jag is not the cheapest thing either. Trust me, my dad has an '85 XJ6 and a '67 (I think) E-Type Coupe. I know these are older jags, but a jag is a jag. I have ridden around in one of these when they came out in 97 or so and they are also sweet rides. Very luxurious and powerful. You have to remember that this car had a $80K sticker new, you will be buying an $80K car. It has twice as much money used to produce as the other cars so you will in turn you get twice the car (just an opinion). I am sure Dan Root can give you a great write up on one of these, I think he is a Jag Lover...

I hope this helps, sorry for the long write up but you asked for it. If it I was in your shoes and had around $40K, I would be an Elise. But if you want a car off your list I would try my hardest to get the Vette. Stay away from the used jag, it WILL break at some point and won't be cheap. It would make a great second car, just not a daily driver. I love the Xfire, but for the price range you are looking at it really doesn't compare. The stang is, well, a stang and everybody has a V6 one. Take it for what it is...