If I was going to get a used 600, I would get the F4. And not just because I'm familiar with their carbs. The F4 was probably the best all-around 600. When Yamaha came out with their upstart R6, all the other manufacturers had to start making peaky engines to compete and it's been going higher each year. Plus, Honda had some drivability issues with their fuel injection the first year for all of their fuel injected engines.