^^^^ newer 1000s get better gas mileage than 35mpg or at least they should. A guy at my work has a hayabusa and he gets 47mpg beating on it.
I might end up getting a 600rr again but I'm still trying to find a good deal on the s1000rr, I found a good deal on the Aprilia RSV4 Factory but I'm not sure if the bike is for me since I can't have a passenger on it.
But on topic with the whole bike size, you should get what you're comfortable with. If you have a friend with a 600 and they'll let you ride it, try it out and if its too much go down to a 250
Some 1000's have decent mpg, depends how you ride them.
A 600rr is the bike I'm hoping to own one day, love them. R6's are nice but stupidly popular over here but if they are better for acceleration then I'd consider one ( still dreaming ) I'm not bothered about top speed just handling and acceleration. Oh, and the Daytona 675 seems rather nice and the new mv Augusta, please tell me you've seen that?
I'm not a fan of aprilla's some look pretty nice but apparently not the best for quality, the BMW looks amazing.
I can't wait to be riding bigger bikes