Top speeds

sounds like good stuff right there, I want to find out if the 120 reading on my speedo is just wishful thinking or not.
Totally depends on how much power you're making and the gearing to back it up.
Even if you have 400hp but 4.88 gears you're going to run out of steam quick. That same 400hp but with 2.76 gears, you'll be a lot closer to the 150 or more mark.
That said, I'm not talking about a 1/4 mile strip. My Top Speed was held for quite a few miles before I slowed the hell down (and then had a F430 go flying by me).