I've rode all cc's of Gas Gas' at expert level for many years. My 2004 280 was by far the hardest to ride, especially in wet conditions. You have to really be on the ball with your throttle and clutch control. The one thing that many people who ride 280's say, is that the back wheel spins so easily. Open it up in 4th/5th gear and you'll see just how much poke those engines have. Surprisingly, the 300 is a different kettle of fish all together - much smoother and rideable.
When my 280's gearbox when wrong, I pulled my old 200 out of the garage and couldn't believe how much easier it was to ride. This was what made me change from a 'big' bike to making a 225 with the 250 S3 barrel. I've been riding it for a year now and it is awesome, so much easier and pliable!
Unless you ride trials where you have to blast up significantly large hills, or you're Adam Raga....a 250 is the max amount of power 'MOST' club riders will ever need. Anything more and you're just making the job harder for yourself. The amount of novice riders I see on 280's is unreal. Back wheel spinning all the time, bike lurching away from them....would be better off on a 125!
Don't get me wrong, I liked my 280. As 'cubby' said, there is always the power there when you need it, and in the right hands they are still a very competetive bike. However, I'd 100% agree that 200's, 225's or 250's are the best tools - depending on what you feel rides best for you
Hope this helps