A 1000 trackbike is hilariously awesome but Scott Rupert once told me that riding a liter bike at TMP is like having a sword fight in a closet. Having first hand experience doing that, I'd have to agree. I had previously told him that I thought riding a liter bike on the Nelson track was like going deer hunting with an RPG.
Anyhow... if your intentions are to just go around a race track, drag some knee, and have fun then a 1000 can be a lot of fun. If you really want to learn how to go fast a 600 is a much better learning tool.. and is easier on tires. Not many people can learn how to go fast on a 1000.
Depends on what you want.
I thought I was quick on my 1098 when I started track days. And I was. But only on the straights. As a mate of mine said; "park and ride". I would advise a 600 for the track but would also add that a litre bike at the track is miles better fun than riding anything on the street.