Originally posted by marshmallow
the 500 does have twice the hp compared to the 250, so it may be better for you if you really like the parallel twin and the overall ergos of the 250. the gs500 doesn't come even close to comparing to the ex:
http://www.formatc.org/ex500vsgs500.htm
if you do prefer the parallel motor, see if you can get a test ride on the 650. so far everyone i know that has ridden one has given it glowing approval. you get the nice design and adjustable suspension for not that much more than a 500.
if you really want to haul ass, get on an inline 4. but if you commute alot, you may want to do the zzr600 rather than the full blown sportbike. my boyfriend used to ride a gsxr6 to work every day and he complained alot how poorly it handled at lower speeds and how bad it hurt his back in heavy traffic. he has a ducati monster now and loves commuting again.
ergos are the most important if you use your bike multipurpose, so sit on alot. you will be able to adjust to a different engine if your body is cozy.