Yeah, when I made the switch from carbed 600 to FI 600, man, lot more explosive powerband and then I flipped the bike. hehe.
Anyhow, what is your area like? Lots of straights? City? curves? good paved roads or crappy ones? I'd say get a 600. Just as fast acceleration as liter bikes and an easier learning curve when leaning. Even though you can lean with the 250, but even then, it has its limits.