The Winchester SXP appears to be simply a 1300 built in Turkey, abeit with a few changes. Nonetheless, in lookiing over the trigger group, the SXP has the same riveted in place shell stops, that were the primary weak points of the 1200, 1300 design. There are a number of changes in external receiver configuration, stock attachment, bore size, and chromed bore finish.
My first repeating shotgun was a Winchester 1200, purchased primarily because it was relatively inexpensive and was the only pump shotgun with interchangable choke tubes on the market at that time. That 1200 saw a great deal of use and the choke tube set up encouraged my early forays into the mysteries of shotgun patterning and shotshell reloading/handloading.
A further footnote: The 1200, 1300, and SXP are the only slide action shotguns, to my knowledge, that do not have an inertia slide lock release system. And yes, the 1200/1300 series are incredibly smooth and fast. I suspect the SXP will be also.