911s will probably compete well but with options you are looking at 110k for that car
Viper is all raw power which is great when you are going straight but I bet the corvette can use all of its power more effectively.
Cayman like all other porsches have looked the same since they day they debuted but you are at least in the mid $70k range for a car that is inferior to the corvette.
In its price range there is simply no competition. I would bet the Corvette will at minimum hold its own if not beat the Maserati Gran Turismo in almost all performance testing which has right about the same HP but costs $130k+...
Honestly the vette is borderline super car level performance and handling at the price (mine was 67k out the door with all the options and taxes, dest fee etc) which is the price of a nice BMW 5 series or MB # class,
If you consider the fact that you can purchase 2 brand new Stingrays for the price of 1 Maserati Gran Turismo I'm really not sure who the competition is for this car!
My 2 cents