Hi and welcome along, I have had a roadster and yes they are more noisier than coupes but that’s part of their charm for me. The 5th bow motor seems to be an issue with them although I never had any issues with mine. My wife also has a 350z vert. Which she loves. As for miles per gallon, think of it a smiles per mile really. You can get up to around 30mpg on runs. My coupe usually makes around 23-24mpg. That’s city driving and motorways, but more city really. Good luck in your search.