My thought from what I've seen over the years... bike setup can be as simple or as complicated as you want to go.
That being said, stock gearing on any modern 600 (2003 and newer) is just fine for 90% of track day guys. I have watched guys as they progress over the years chase their tail with gearing. Normally, "it's too tall" when they are in Novice/Intermediate so they shorten it up a bit. It might help them a bit, but then they'll progress to the point where it's hindering them. At that point, the once seemingly "too tall" gearing now starts to makes sense. Gearing for the theoretical top speed is never a consideration by any fast rider.
It may sound harsh, but it's reality. As long as your gearing isn't wildly radical from stock, the gearing isn't the problem. It's not the gearing, the tires, or the bike, it's the rider. Obviously, having a clean, maintained and tech-ready bike is implied here.
If you're in Novice, Intermediate, or even a new Advanced group rider, you'll benefit far more from improving your own skill set to be consistent then continually messing with your bike. What encompasses being an "Advanced" group rider? Being consistent on your lines, hitting your apexes, ability to set up and execute clean passes, and eliminate a large portion of 'coasting' while circulating on track. Is that an easy task in itself? No, that's why it's called Advanced after all. If this stuff was easy, we'd all be Advanced riders. But if you're in Novice or Intermediate, I can promise you there are several things that you can work on that will provide ten fold improvement in your riding, lap times, and safety than pissing around with gearing will ever net you.
You have to know your audience and who you're asking advice from. If you ask the Apex/ Team Hammerhead racing team gearing advice on their 675's, they might talk to you for 45 minutes on what to do. But those guys are at the very pointy end of the 600 class, where every little thing begins to matter. If you're running 20 seconds+ slower than them, none of the things they'll talk about really matters.
You can have the most perfectly set up bike for a given track, but it ain't gonna do shit for you if you aren't consistent and can't hit your apexes.