I've narrowed my choices between the gixxer 600 and cbr600rr. I've sat on the gixxer and it fits like a glove (im only 5'4"). Its also cheaper than the cbr, but the cbr is more tighter and nimble and also has a higher seat height. Decisions, decisions...
I have both the 07 CBR & the 08 gixxer and here's my 2 cents. I don't race or do track days, just street. My feeling is the CBR is slightly more technical than the Gixxer. Here's why I say that. I'm 5'2" and it basically came down to the CBR being more difficult with the extra height (even after shaving the seat; which can't be shaved much) and touchy throttle. Getting the CBR into my shed over an uneven gravel drive & up a 2-3" wood incline was tricky. Getting on the throttle so it didn't kill but enough to get it up into the shed, then braking quickly was a bitch. I thought I was going to have to lower it, but was really concerned about messing with the suspension. Once I saw & sat on the '08 gixxer, it was all over with, and I sold the CBR to my husband (who has the same problem getting it into the shed, but has a little extra leg length to catch it if it kills). I've never regretted it! The Gixxer is more user friendly. I LOVE the stock gixxer tires. I never felt the difference in the weight between the 2 bikes. I like the extras with the Gixxer like some tools (even if the usual crap) and the rear seat cowling. The gixxer mirrors have more vibration, but it didn't bother me that much and I like the looks of integrated turnsignals. The gixxer takes regular unleaded, but I got better mileage with the CBR. The gixxer headlights are fabulous, I really like the gear indicator, and the emergency flashers. After market parts for the gixxer came out much sooner than the CBR. Tons of gixxers out there for used parts. The CBR left me anxious (granted, a lot of it at my driveway). The heat from the undertail exhaust is noticable in hot temps (but I do love the looks). The turnsignals are rather old-fashioned looking IMHO, but those are easy to change.
The comfort is about the same on the 2 bikes. I can go about 3 hrs before needing a stretch. Their ergos are very similar, although I don't think the gixxer seat matches a woman's butt very well, so I'm having a friend reshape it (the seat, not my butt
So far as mechnical, I was really unhappy when the seat screw on the CBR wouldn't come out. Fortunately I checked the forums & didn't completely ruin it before finding out about the problem. But that was on a 2007, and it's probably fixed now. On the gixxer, I had the bad O2 sensor & have the water in the headlight assembly that needs fixed, but I still prefer the Gixxer for me. I've been very happy with Suzuki's warranty response.
Going from the 500 to either of these bikes, you'll feel a HUGE difference. I went from the Ninja250 to Suzuki GS500F to SV650S to CBR to the gixxer. I know now that tiptoes isn't enough for me, I need the balls of my foot on the ground to feel okay. That's just my personal limit & allows some room for the unexpected. I ride to have fun, not to be anxious. With the '08 gixxer I feel like I have the bike I've always wanted.
Okay, maybe that's more like my $2 worth, but hope it helps.
Good luck with the decision! You're going to have a blast whichever way you go!