Been to IPSC Shotgun World Shoot 2015. Supernova is massively the most popular gun, like 80-90% in all Standard Manual division. All 3 top 'Magic Finn' shooters used Supernova, about 6-7 of top 10 shooters.
Benelli is definitely a good gun.
As for Winchester SXP - also a good gun. I'm shooting 1300 myself. But you won't be able to open the loading port because of trigger assembly design. Not good for strong hand Load4. But it's open enough already for weak hand Load.