turbo or cam?

if you went with a cam, to get it's full potential, you'd probably want to increase your compression too, which would mean new pistons and decreases fuel efficiency. supercharging would give you parasitic loss if you're on the highway and cut your milege, but would probably be the easiest to install. if you're going to spend a lot of time on the highway (when you say highway, i'm thinking like interstate, like traveling to and from college or something like that where you spend hours at 75 mph) i would recommend a turbo. you get the boost when you need it, but it's not going to give you as much parasitic loss when you're just cruising. look at the semis that spend all day on the highway. they use turbos to give them the power they need to accelerate all that weight, but you need the best fuel economy possible when you're driving 100k miles a year. if you know someone with a turbo DSM, you might be able to get their stock turbo if they upgrade and run around 8 psi on yout stock internals.