the two big bikes that i have ridden are the RM-250 07 model and dam that thing had balls, she was all go or nothing
thats an experience everyone should try, get it in the rev range and bam your off and un-doutably on the back wheel all the way through the gears
the only thing that i didnt really like about it was the simple fact the i was used to 2banger
so cornering and being down the bottom end still had pull but i dint like it that much...
the 2nd bike the KXF-250 on the other hand was a completely different story, that thing being and 08 model dam it had some punch.. being used to a 4banger that thing was some much easier to ride on the dirt and there was always that element of usable power there, where ever you were in the revs you could twist it on and it would pull like buggery!
buying a big bike to ride off road whilst still road reg. doesn't really appeal to me, id rather have a road bike or a dirt bike... thats just me and everyones different and thats just case they road bikes and dirt bikes each have there advantages so one day id like to be owning both
good luck with the buying man, probably didn't help but thats my experience and opinion for ya