I was very excited when the 830 came out. The features sounded great and I've had VERY good experience with Bernina machines, albeit that was 15 years ago. Plus I have a very fine dealer just minutes away.
Went and tried the 830. Lots of nice features but was singularly unimpressed with the stitch quality: sewing, embroidering, or decorative stitches. Tried a variety of different threads, fabrics, stabilzers, etc. I had the (very helpful) salesperson thread the machine a couple of times just to be sure it wasn't user error, but the stitch formation was still never quite right not matter what I did.
The 830 is also very finicky. Likes some threads and not others. Has a very specific way to thread and if you deviate, it chokes. If the thread is not just so on the thread stand, it tangles.
Since stitch quality is, for me, the primary measure of a machine, I opted not to get the 830.
As far as the Creative Sensation, it sounds very interesting. I have the Creative Vision 5.0, with which I have a somewhat tense relationship. Sometimes it cooperates, sometimes it doesn't.
Many of the issues with my 5.0 were fixed with the 5.5, and many of the features on the CS have been on the Viking Designer Diamond Deluxe for over a year now, so it's not an entirely untested platform.
The Active Thread Technology (?) is particularly enticing, if it lives up to the hype. So I'll try out the CS and see if it becomes the replacement for my 5.0.
You've probably heard it before, but the key to deciding on a machine is to test, test, and test some more. Take samples of all of the different kinds of fabric you sew on, don't just use the samples in the shop. Make up some quilt squares complete with batting and fabric and do a LOT of free motion at the speed you're used to. Cut some triangles and piece a 1/4 inch seam. Do the feed dogs grab right away, or do you get a little knot of fabric and thread at the beginning?
Take some heavy denim and see how the feed system handles a folded hem over a flat felled seam. Sew 18 inches of a decorative stitch, then sew another row of the same stitch right next to it. Do they line up? Does the fabric pucker badly? Try all the button holes on a variety of fabrics. Embroider a couple of small samples on different types of fabric. Does the fabric pucker? Are there skipped stitches? Do the outline stitches run along the edges of the filled areas correctly?
Make notes as you go, then go home and look them over. If you spend less than 2-3 hours in the store, you're not doing it right. Think about the experience. Go back another day and retest as needed before you make your decision. If the sales people get unhappy, it's probably best to find another store.
In short, put the machine through the ringer. It's a lot of money to spend and your sewing time should be spent enjoying what you're making, not fighting with your machine.
R