As a 675 owner i will say that they are a little more fragile than the big 4 600's, but they're not terrible. There are annoying things that tend to happen on the 675, but they're not insurmountable.
That being said, the most reliable of the bikes you mentioned is going to be the CBR. This is not to imply that the R6, gsxr, and kawi aren't going to be reliable, it's just that honda tends to make a rock solid bike that is well engineered and well built, sometimes at the sacrifice of extreme performance--though i think the 600rr is the best 600cc inline4 superport on the market.
while i think the 650r is a good bike (along with the sv650), i don't really classify them as being in the same performance range as the other bikes you've mentioned. I'm not saying the R6 is a better bike for you, but there's a remarkable difference between an R6 and a 650R, one of which is power delivery, but also other performance and comfort aspects. You very well may be happier with a SV or a 650r, especially if you're doing more freeway and city riding.
I rank the big4 600's as such taking into account reliability, performance, comfort, build quality, price, and looks.
1. 600rr (pros: build quality, comfort, performance, looks, reliability. cons: high price)
2. R6 (pros: performance, looks, build quality. cons: price)
3. gsxr (pros: reliability, comfort, price cons: looks, build quality, performance)
4. zx6r (pros: price, performance cons: build quality, looks, reliability)
keep in mind that the differences between all 4 are very minimal. the biggest difference is looks and price. they all perform, they're all pretty reliable, and they're all built well on an absolute scale.
oh, and GET SOME GEAR. the world doesn't need any more road hamburger and totalled 600's.