Think about what type of rider you are as well as the tracks. I just sold my 600cc (636cc actually) trackbike as it wasnt that much fun to ride. The litre trackbikes are fun to ride but you are looking at a a set of tyres every weekend if you are racing it and the first highside is likely to be a big one.
What I like about the Superduke is the handling on the brakes into, and the low down friendly drive out of the corners. I know the SD will never rip snort down the straights with an S1000RR but those goalposts move every year and pretty soon a GSXR 1000K8 will be down on power too.
I am too old, slow and lazy to be dancing on the gearlever like you have to on a 600 and hated revving the thing to 14000rpm just to keep up. So the SD suits me and my limited aspirations, At the other end of the scale I saw a good rider (Rob MacNealy) at Lydden once on his 06 SD battle bike and he was passing the latest il4 thous like they were stood still. Lydden is a short track, almost all corners and mostly 3rd gear. I reckon MacNealy just stuck it in top and did the whole lap sideways, being an ex Supermoto racer probably helped. Anyway, until I can ride like that I dont need anymore that the SD has.