Hey Njfife,
I personally own the new Ninja; 09 Ninja 250r. Regarding your motorcycle issue I would go with the 500 over the Katana. As Spool mentioned the Katana has a 4 cylinder 600cc. The cc isn’t much of a problem because I have also test drove the Ninja 650r. The 650 has 2 cylinder engine making it easier to ride compared to a 4 cylinder 600. If you are worried about your weight then I wouldn’t recommend the Ninja 250r. It all comes down to your experience and comfort zone. If you don’t have much experience then go with the 500. The best thing to do is try to test ride one before actually buying. That usually makes the breaking point on deciding. If you can’t test ride one then at least sit on one and see how it feels, check how low it is from the ground, etc. Comfort is important, especially for big guys. Hopefully that helps.