I shot my Xtrema 2 KO Slug this past weekend. I tried the following through it:Hastings 3" 1900 fps, Hastings 2 3/4" 'low recoil' 1000 fps, Federal Vital Shocks 2 3/4", Winchester 2 3/4" Xpander, Remington 2 3/4" Copper Solids, Remington 2 3/4 Buckhammers, Hornady SST's (2 boxes, 1 for sighting in, one for testing), 3" Lightfields.
I fired from 100 yards using a sandbag rest. Winds were non-existant, in fact it was trying to be a bit foggy. I fired 3 shot groups with the same hold point for all three shots.
Results for MY gun were:

Remington Copper Solids 2 3/4" shells - 1.3" group @ 100yds
Hornady SST's 2 3/4" shells - 1.75" group
Remington Buckhammer - 2.25" group
The worst group of the bunch came from the Hastings 3" 1900 fps jobs. They had an 8" group. Next worse were the Lightfields.

I had similar results last year with the 391 Urika barrel. The Remingtons worked the best, w/ the Lightfields being the worst. I'm guessing the Beretta barrels just don't care for the Lightfields for some reason.