I own a SX3 and I love it. To my knowlege it is a complete redesign. I know SX2 barrels do NOT fit a SX3. From what I was told, FN, (who owns Browning and Browning is who owns Winchester), was going to make this shotgun design the new line for Browning. FN excutives decided to use it to jumpstart the ailing Winchester shotgun line. It is the fasted shooting autoloader. I love mine, it is balanced well. Shoots 2 3/4 to 3 1/2 with out a problem. Manageable recoil even with the 3 1/2 shells. The camo finish has no maintence, other than a wipe down. Field stripping is easy. The gas blowback does get plenty dirty though. But I would highly recommend it. One draw back is a deer barrel for it runs about $700 bucks!
Several of my hunter friends have this same gun and they have reported no issues. Great gun. I think the top clay shooter is rep for the gun and has a great vid on youtube shooting 12 clays in some amazing amout of time.