I can win every F class event that it's eligible for with it. If you don't want to / can't do that, try a private lobby online vs. AI where you can choose the opponents' cars, or just run a few laps in Rivals mode.
Even if you don't win, you still get the exact same amount of XP so you'll still level up your Hummer affinity.
Has anyone done this
Yes, but not me personally.
and if so is it useful?
Fully upgrading a car is NEVER, EVER a good idea. This game puts cars in classes based on PI (yeah I know you already know that, I remember you from FM3.) A car when fully upgraded is almost guaranteed not to sit at the top of a car class, and is absolutely guaranteed to have more power than the car can handle and therefore not perform well against competition.
The Hummer in particular can be class limited in 5 classes, F through B, and due to it's immense weight it performs worse in each consecutive class.
Instag8or ran the Hummer against a Prius and a late 70s Mustang (in F class) in one of his Hotlap Challenges. I was the only one to run a Hummer, and I'm not the fastest guy there, but neither the Prius nor that Mustang top the leaderboards anywhere so the times you can find in that topic will give you an idea of how a tuned Hummer compares to the competition. Here's a link to the topic: http://www.gamefaqs.com/boards/997653-forza-motorsport-4/60810428
and how fast can it go?
It's top speed is abysmal, because it has the worst aerodynamics of any vehicle I've ever seen.
In terms of lap times on an average track, which is a much better way to determine a vehicle's usefullness in Forza, check the link I posted above, and assume that it's worse the further you upgrade it.
Because of the difference in skill level in that topic, I'd think it's safe to say that the Hummer would be 2-3 seconds slower per lap against an average car, if both are tuned well and driven by drivers of near-equal skill. That's on a track where lap times average close to 1:30.
One positive that the Hummer has is it's immense torque, from the Duramax Diesel engine. It will beat just about anything off the line, but only for a very short distance.
People online also seem to be scared s***less of it.
Just ignore him, he's from Quebec. - rammtay, on the GameFAQs Canada board