Welcome SXGT!
Yes this site is dedicated to the 08+ Ninja 250R, but as you can see with just a quick look, there are a lot of us, myself included that have moved on to other bikes, but we still share and contribute as this place is just like a family. So, long story short, no bike is excluded here, but the core of the site is the 250R.
As far as being good enough on a 250R to take down others on bigger bikes in the twisties? If you're good enough, it is very easy!! A number of times I have taken on some Buell 1200's and after a couple of corners, they are way behind!
Always remember this....A great rider on a slow bike, will just about always beat a good/poor rider on a faster, more powerful bike in the twisties. Long straights are another matter altogether, but thats not the question!!
Check out the following vid of a fellow 650R rider like me(but this guy actually has riding skills!!

) trying to chase down a 250R rider on a track in Thailand.
YouTube - ER6n Hot Lap Pirelli Track Day BIRA Circuit Dec 26th 2010
This shows the differences quite well, plenty of speed to gather him in on the straights, but in the corners, the 250R rules!!!
Don't forget to tell us more about yourself, and throw up some pics of your bike before some of the others start yelling at you!!!!