I am not an expert. Been riding track for 2 years and this year a couple of times on an SV650s 2004. An expert who builds race bikes told me that the earlier frames were better, but I did not want a bike without fuel injection. I upgraded the suspension with Racetech springs and a Penske rear shock, which I would highly recommend. Had them installed by an expert and tuned to my weight. Do this if you are going to ride track. I makes a huge difference. My bike is a blast to ride now even on the street. Brakes are not that great and I am still getting used to the bike, especially the brakes, which need upgrading. First thing to do is replace the old rubber brake lines if they have not been done. I was looking for a 600 or 750 but this bike was so much cheaper to buy and own, I opted for it. You will find on faster tracks that the liter bikes and 600's are going to blow by you on the straight I tend to start cruising around the track unless I have someone to compete with. But that is just me and I plan to adjust next track day. One thing about these old bikes is that they have probably been dropped and/or crashed so inspection is very important. Look for cracks in the frame with a flash light. Try to check the alignment with the string test if you can. I plan to get GMD Computrac to look at my bike at some point although it is handling okay. The subframe is out of alignment. As you know, motorcycles turn into projects and you will spend money one way or the other. But you can do a lot of your own work on the SV650. I pull wheels, replace calipers, and will soon do sprockets and chain.
Throwing my vote in the SV650 column as well, but I might be biased because I've got an '03 that I hurl around in "I" and possibly "A" soon. There's nothing that makes you feel quite as awesome as zipping around literbikes in the corners! On the cost front though, while the bikes are a lot cheaper to buy the ongoing costs are still pretty similar to something bigger. I started with an SV because it was cheaper, but over the years I've put $3k into the suspension and brakes anyway. And tire selection can be limited, the best track tire I've found for the SV650's stock size is the Pirelli Supercorsa SC2 rear/SC1 front. They're not a street legal compound (although they are DOT grooved), so you can pretty much only buy them from trackday and racing providers. Revzilla and the like don't carry them (They carry the street-legal SP version, but that doesn't come in the SV's size). Some have gotten around this by swapping on a GSXR rear wheel, but then you lose some of the advantages of the SV's nimble handling.
I started on a Ducati then dropped to a GSXR750 then to an SV650 (2nd gen). And I'm a better rider for it. Like many have said, this is a great track bike. Cheap and easy to work on. Plenty of easy to find parts. Well established tricks/tweaks to get the most out of the bike. And because it is low on horse power, it forces you to work on your lines and being smooth. You can get past 600 and even 1L but you will need to ride a lot better than they do. Later, once you've developed (confirmed) your skills, you can always upgrade the bike. At that time, you'll also know a lot more about the type of rider you are and which faster bike might suit you better.
Get both, starting with the SV. By the time you figure out the SV, you'll be ready for the 600, and the SV will be an awesome back up bike. Whenever you get stuck in your development on the 600, go out on the SV for a couple of sessions (or a day) and you'll make another step on the 600 when you get back on it. Been doing that for many years now.
This is a great thread I've enjoyed reading everyone's comments. I personally bought a track ready first gen SV650 5-6 weeks ago. It took me from novice to advanced group in 3 track days. I do not think I could have progressed that quickly had I started on a 600. But now that I am in advanced I am still having an absolute blast on the SV but having thoughts on selling for a 600. Wish I could have both!
SV's are wonderful bikes but the suspensions are weak so if you get one you'll likely want to upgrade the shock and fork internals after while. Or just buy one that's already prepped for racing, that'd be the way to go.
LOL. You mean the meat grinder class because that first turn after the green flag is thrown is like tossing you and your bike into a meat grinder. You just have to make sure your health insurance premiums are paid and that you're married to the kind of woman that wont complain about doing all the housework until you heal.