Hardly the same comfort as a factory c6 z06 have you heard the literally 2-3' long exhaust on that thing? and their resale is piss poor at best....
That said they are sweet and if I had bill gates like dollars I would buy one to build and play with- I actually looked at them hard before I got my c5z.. the kit claims you can build it for 40K but most guys that have built one have about 80K in them.
To the OP, take this with a grain of salt, but the one car people typically buy after selling their c5z and don't look back is the lotus elise. Don't ask me why I have never driven one but I read this all the time on corvette forum... a lot of guys will buy c6s or even c6 z06s and then either sell them after a short while and get a c5z again or keep them and add another c5z to the collection. I should probably drive one but I don't see me trading mine for that carbon fibered camry (joking doc ;-) ) any time soon- they say something about the c6 missing the raw spirit of the c5z that the lotus has? I hardly call my c5z raw but I will admit my dad's ls3 c6 does feel tame in comparison and it has more hp and only a little more weight.... it probably has something to do with the "tossability" of the elise as the corvette is sort of broad shouldered and daunting from the drivers seat... points to ponder
I wouldn't even look twice at the GTR- the ZR1 is pretty sweet but unless you are going to road race it competitively, or are making a collection of rare cars, I would just put a well-proven A&A or ECS blower kit on a nice low mileage c6z and pocket the 60 grand and smoke one at the drag strip if you could hook all that power... Actually a c6 z51 ls3 car with a blower is an even closer powerplant and would cost you another 10-15 less yet but I do like the body kit on the z06 and the weight reduction measures.
I won't touch the porsche/corvette/german/usa topic- been down that road too many times on here kickass;-)
I drove a few m3s I will +1 the meh- if I were to buy something german along those lines it would probably be a used amg sl55 or sl65 as that car is stunningly beautiful IMO...
That's my .10 cents.