I wouldn’t write off the GS500 because of air cooling…they have been around for over 20 years, and are one of the more reliable bikes out there…of course I am biased, but I don’t think a bike would survive if it was a piece of…
I just finished my first ride on my GS and I don’t know if I would like a bike with any less power than it has. The 200cc bikes from the course are good for around town, but as soon as you hit any kind of speed, they loose steam…but the bonus is manouverability, man the light bikes turn on a dime and make change…I haven’t sat on the Ninja 250, but I sat on a Ninja 650R and it was tighter feeling than my GS…I’m 5’11” so not that far off of your height. Like Jeff said, sit on all of the bikes that you are considering…think about how they all felt, then go sit on them again…remember that you will probably be sitting on the bike for an hour or two when you are riding, so try to imagine if you would be comfortable for that length of time in the saddle…
I thought my GS500 was pretty roomy, so I bought it…after sitting on it for a couple of hours today, well it wasn’t bad, but it could have been better…
It will come down to what you prefer…you can alway just stop more often…you need to like the bike that you are riding. It is part of what puts the smile on your face when riding it…
Take your time making your decision and have fun…
Good Luck!!