Racing...
The SXR is about 80 lbs heavier but 20hp more powerful. The extra HP more than makes up for the weight. The SXR weight increases it's traction and hook up in heavy chop as it doesn't pop out of the water as easily. This also gives the SXR a cornering advantage. The extra width increases the stability in the corners, the tray width gives greater rider control, and the weight keeps the boat in the water through rough conditions and in the wake of another ski. The SJ is going to be more competitive with front sponsons, ride plate, etc, but mod for mod, the SXR is a much faster hull design over the SJ. If you plan to strictly race, there's nothing to ask, the SXR is the faster design hands down. It is a smoother ride, that is much easier to learn, control, and ride at high speeds. The SJ is almost as easy to take a cruise on as the SXR on flat water, but in chop, the SJ will effortly cruise at about 25 while the SXR can effortly cruise at about 35 (due to chop pop).
Free ride/surf...
The extra HP of the SXR cannot make up for the extra weight. You are going to have to crank some serious low in power in the SXR to move it around like a SJ in the flat water. Even then, it's a tank and will never feel like the SJ. This is less of a problem in the surf, but the SXR wants larger (3'-4'+ clean peaking surf). The SXR will plow through smaller weaker surf. Wave for wave, the SJ dominates the SXR. In flat water, the SXR isn't even worth talking about.
I personally own a SJ. I was looking at going to a SXR, but I found that increasing my rider skill allows me to compete against 1 or 2 skis in flat water at a reasonable level. A few mods (ride plate, sponsons etc) will put me at a good level to compete with stock SXRs. My goal is to keep my ski performing at all RPM rangers, rather than just all low end like most SJ owners here. I want my ski to take a bouy course, then ride the surf, then work on flatwater 180s and such. If I never planned to doing anything but racing, I would have switched to a SXR, i was going to, but I don't just race, so I decided to stick with my Superjet. I wont have the best performing boat in any one condition, but I will have a boat that will perform well in all conditions.
EDIT: I'm rebuilding my X2. It will be set up to race buoys. Once it is done, I will shift my SJ to more freeride/low end set up. If I am not please with my X2 after the rebuild, I will sell it for a SXR, keeping my SJ for free-ride/surf and setting up the SXR to race.
