wheelbase, and i don't think it affects performance becuz the 2+2 is about 200lbs heavier, but there is much much more room in the 2+2 and in my opinion the 2+2 looks better becuz it is longer which gives the Z more of a sleek look, (that is what i will miss on my 2+2, i am selling and getting a Twin Turbo) but other than that I also know that the 2+2's insurance for me is $30 bucks cheaper a month becuz it has four seats!. I say go with the 2+2, you won't regret it if you arent getting a Twin Turbo.