I'm looking to buy a used 2007/2008 Nissan Altima Sedan, and am split whether I should go for the fuel economy of the 2.5, 4 cyl engine (26 cty /34 hwy) or the power of the 3.5 V6 (20 cty /28 hwy)? I can get all the options I want (heated leather, sunroof, etc) with the 2.5 model, but...