I sold my 500 this year, had been riding it for over 10 years. Bought a project 550 and got it going over lockdown, so able to make a reasonable comparison. In my opinion, the handling was the same, but forks didn't top out like 500, small difference. 550 was noticeably smoother, but that could just be the difference between examples and not a general thing. 550 had a bit more poke up to about 6000rpm, noticeably more above 8k. 550 gearbox slightly slicker, but neutral harder to find. My 500 originally had a problem jumping out of 3rd, but once cured gave no further trouble. Had a 500 when I was young and stupid and I could make the clutch slip when giving it heaps, but don't mistreat my bikes anymore, and as has been noted 500s are fine under normal use. Instruments look a bit nicer on 550, but 500 ones are fine. I think final decision will come down to best example you can find within your budget. Good luck.