The 2008+ SJ handles really well on a race course, as good as the SXR. The difference is the SXR is easier to ride. More Stable. The SJ has to be ridden very aggressively. It will carve as good as the SXR, but you will get tired much faster on the Superjet.
Now, if you just want a good ski to ride, The 96+ Superjet will do it all. slap a long ride plate on there and Worx intake grate and you can go carve bouys, the ski does not lean into a turn like an SXR or SXI Pro, you have to learn a different technique, it is more flat turning, but you can still have a blast ripping bouys. Keep in mind from 1996-2003, Most racers raced Superjets, that changed after 2003 when the SXR came out, then you rarely saw a SJ on the tracks.