Couple of people have asked, so I thought I would write it up. Not SV related at all, but I know people often move on to SS600's after the SV so it might be useful.......
I was going to do a write up on this after saturday, as I have now ridden both on the track.
At the moment, I prefer the R6 on the track! It's probably a little biased since I have had much more track time on the R6 than the 675, but out of the crate, the R6 has a better track setup. From my experience, I have pushed the front end on the R6 just as hard as on the 675 and it didn't let go. There are tonnes of little things that may have contributed - I probably should have dropped my front tyre's psi a little more for the track; maybe the tyres weren't quite up to temperature etc.
However, the R6's suspension felt a little more compliant; more fluid and able to deal with subtle bumps. Coming round Gerrards and hitting some of those mid-corner ripples for example and the front end didn't falter on the R6. By comparison, the 675 feels much firmer and less forgiving.
The geometry of the 675 is much more front-end heavy than the R6, which may have contributed to my low-side. Quite a few peeps (racers + trackdayer's) from the 675 forum have said the same and would highly recommend getting some suspension work done. They say that it is quite common for the front end to tuck without warning - which is what I found, whereas I could feel the front end's on both the R6 and GSXR-600 k7 slide a little - especially if I had overloaded the front in corner from running in too hot.
Where the 675 does eclipse the other 600s I have ridden, is the engine
Coming out of turn 12 at Eastern Creek, I passed so many 600s (well ridden 600s) on the exit of the corner because of the torque and drive. Despite top end power being fairly similar, the grunt lower down meant that I would really launch out of the corner. A guy on a track prepped 05 R6 in my garage followed me for a bit and he couldn't get close on the exit, when picking the bike up and rolling on the power. The engine also sounds pretty sweet - especially if you are a twin fan. I have to admit being more a fan of a 17k screaming R6, but I think the triple sounds throaty and unusual.
Size-wise, the 675 feels bigger than the R6, but I don't think there is much in it. The seat compared to the tank is lower on the 675, so you feel more sat in the bike than perched on top like you did with the R6. Build quality, there pretty similar, though I'd probably say the Yamaha has the edge. 675 comes with a gear indicator in the clocks, which I don't use much on the road, but is great for the track. The lap-timer is much better and records splits on the 675, whereas the R6 just records the last lap only.
One last thing worth mentioning is spares - A lot more R6's are raced in the UK than 675's, so picking up cheap spares of ebay is much easier - something worth thinking about if you are planning on taking your bike to the track in road trim.
So, at the moment, the R6 has the edge, but I'd imagine that will change after a few more trackdays and this suspension work