hi, I did the same as you last year, also needing the extra power
Turns out, I didn't really need it, but I'm still happy with my decision.
All I would suggest is keep hold of your 600 too, I wish I had.
It's the same every time you trade up, you miss the old one because of all the things you could have done on it (like my old bike, I don't want to do wheelies etc to protect the bearings, chain - you know what I mean. wish I'd thrashed the 600 more
I asked the same question when I stepped up, what I remember:
check the exup, ask them about it, if they're good, they'll know what you're on about
that's about all I remember
I'm sure other will be along to be more use than me
Tom