I wouldn't compare the two, they're two different animals.
If I were you I'd tell him: "yours can go fast, but mine can go anywhere"
When my sports car friends make comparisons, i usually offer to race.
"i will race you any time you choose"
"you pick the time, ill pic the track"
then i usaully say something like we can go to the mall, and race accross the parking lot... straight down the center over all the medians.
For the record i really love the FRS and i almost bought one, but i can not afford both. And the FRS cant do anything practical, minus saving some fuel. I love they way they drive, and handle. But even as nice as it is driving one every day becomes a chore, in the truck its the opposite. The more you drive your truck the more it gets less annoying (not really good example since i have always liked driving my trucks just in general) no stress over potholes, less douchebags trying to cut you off or get in your space on the road, dips arent an issue, when it snows your not shit out of luck. This apples to oranges comparison is pretty much useless. The only way i could ever be more attracted to a car over a truck of any kind as my ONLY vehicle is if i had no life, nothing to hual, nowhere to wheel, drove 100 miles a day, and lived somewhere tropical. Other then that some form of truck or SUV even with the shitty MPG will always win out in practicality and liveability to me.
Now i could justify this if i had an old street legal truck that worked well and the new fun car DD. But i would still pick a nice truck DD and a old beater play car first.