I have a Sixxer, my Bro in law has a R6. I like the lines of the GSX-R far better, I like the incorporated turn signals and the seat in my opinion is a lot more comfy stock. Mine is an '05 and his is an '04. The GSX-R sits more natural to me.
Notice How I am saying ME, ME, ME. Get the point. It's really what's comfortable to YOU. Don't worry about power, and speed, these newer 600's are outrageous on the power scale for their size. I am looking to step up to a 1000 just because the wife likes to ride along, and we plan on taking really long trips, so it would be nice to have a little more low end torque.
Go with what you want, the spec's on these bikes are already crazy for the price.
Ohh on a side note. Suzuki's come with the Passanger cowl if you like the look. Yamaha's you have to buy it seperate. As well as the dampner. I think you get more bang for you buck out of suzuki if its comfortable to YOU.