The SJ has a much smaller feel the the SXR. You will like it better than the SXR for the kind of riding you do. The SJ is going to feel like a tank compared to the 550, but it's going to have much much more potential for power, which very much makes up for the weight. The SJ is also a lot more stable than the 550 which will allow you to set up better for jumps and tricks. Look at the aftermarket hulls. Wide and short. The BOB is based off the 300sx I think but everything else is wider than the 550.
The 2008+ SJs had their chines deepened to allow for better handling and cornering. The new models are going to be less loose in the back. I have only ridden on the one time and it didn't slide out in the back like my 2004. It handled ok and with a Jetmaniac BB in it it jumped amazing. The 96-07 skis are going to feel looser than the 08+ skis. The 08+ skis also have built in front sponsons which make it more stable, but you can just add tubbies to the older model superjet.
The 96-07 or 08+ SJ will probably work just fine for you. The 96-07 would save you a lot of money over that 2012 model and would be very loose in the back. If you want loose, you should go with the older model, and put the $5000 you save into big power. Selling the SXR and 2012 SJ would give you enough money to buy a 96-07 SJ, customize it from the ground up and have enough power to make up for any weight.
just kneel in the tray of the SXR. It feels massive to look over. You don't need to ride it to know it's a tank. it's a race boat and not going to get loose like a 550 ever. Kneel in the tray of the SJ. It's going to feel big compared to the 550, but if you think it's going to be manageable, then know that the extra width is more stability and more room for more power.
In the event that the SJ still feels to big, the way to go is a FX1. Look at the videos from Daytona. The guy that rides the Frankenstein ski shreds that thing. If you want little, go with a 550 conversion or a FX1 conversion.
At the end of the day, considering your budget, you best bet is to go with either the SJ or an aftermarket hull. It sounds to me like you might like the looser feel of the older 96-07 SJ and the extra money spent on more power, than the newer SJ with less power.
Remember, It's all about power to weight. The SXR is a fat pig for racing that will never have enough power to justify the weight. The 550 takes too much work to convert and doesn't have enough space for big power. Aftermarket hulls and the SJ are in the sweet spot you are looking for.
Edit: BTW, the SJ is a similar feel in size to the 650sx, but the SJ is much more stable, handles better, corners better, keeps the water out better, has more power upgrades available, a better pump design at the cost of only a few more pounds. The SJ makes up for the few extra pounds (like 10-20) by having a vast selection of aftermarket parts that are lighter than stock and produce much more power. If you like the 650sx, you will love the Superjet, especially considering how many options there are to customize it. I moved my X2 motor to my 650sx last week. I rode the SX and all I thought was that it handled like
and who designed this
ty pole and hood? It felt the same in size, but there was no comparison in quality.
However, don't place judgement on the SJ right away. the stock 701 motor isn't a lot to brag about. A pipe, head, prop and intake really wake it up. Some light motor work doesn't hurt either. That's why I said to buy a 2000 model and put the extra $5000 into the motor than the 2012 model more stock.