hp is always way more expensive for the next one than the last one... get the 210 and then you can upgrade to the 240 later... the jump from your current bike to 210 is bigger and more noticeable than the move from 210 to 240 would/will be, and you have to ride it that much harder to use those last hp...
the real problem is always second guessing yourself - just ride your existing bike really hard all the time for a few more months then go for the 240 with the extra $$$ you've accumulated... your problem will be if you go 240 and aren't silly happy you'll be depressed that you spent the $$$ and if you go 210 and aren't silly happy you'll lament not spending the extra $$$... life sucks when you think too much - ya just gotta do the pros and cons of each and then pull the trigger and go ride...