There are a few problems with the SPX. First, it's not threaded for chokes - I've seen a lot of guys have problems knocking over steel with an open choked gun.
Second, it only holds 7+1. You really want 8+1. Reloading time is the name of the game in shotgun stages, and that extra round can make a big difference. If you want a 930 a better option is to buy a regular 930 for a lot less money, then send the barrel off to Guncat (he's a member here) and have him cut it down & rethread just behind the ports. You need to get rid of the ports unless you want to run open class. I had my 26" field model cut down just behind the porting to 22". Guncat (aka Rose Action Sports) does very nice work, quickly, and at a very reasonable price. Then add an 8 round Nordic tube and you're in business. You may want to weld up the lifter, also.
Finally, most people find the ghost ring sights on the SPX to be slower than a plain bead. That's just personal preference but a lot of people find it to be true. I added rifle sights to mine.
You probably know this already, but if you run an x rail or roadblocker brake it will put you into open class, just like the factory porting will. Then you'll need an Open rifle & pistol to be competitive.
You'll end up with a better shotgun than the SPX for a lot less money if you go this route. Brian Enos forums has a lot of info on the 930 if you're interested. Feel free to PM me for more info, I'd be happy to share. Here's mine - I have about $600 total into it: