As far as I know, the main difference is that the Optima has a slightly larger bore diameter (about .730" I think) as compared to the standard Beretta bore of about .722". Naturally, this means that the Optima choke tubes are a different size from the standard (Mobile Chokes I think they're called) Beretta chokes. That way, the choke tubes will not interchange. 
The Optima also is a little heavier in the front end due to the larger diameter barrel. The wall thickness of the barrels are the same, but the diameter is bigger on the Optima.
Oh yeah, one other difference. The Optima has the letters OPTIMA stamped into the forend wood. Looks gaudy to me, but that's just my opinion. I've heard that some of the Optima's are having problems with the rib shooting loose or curling up. I think the rib is plastic and somehow the rear end is curling up on some of them. Don't mean to scare you, but that's what I've heard from reliable sources. Beretta has been pretty good about replacing the ribs, but you've got to send your gun off and wait on it to be repaired.
The Optima also is a little heavier in the front end due to the larger diameter barrel. The wall thickness of the barrels are the same, but the diameter is bigger on the Optima.
Oh yeah, one other difference. The Optima has the letters OPTIMA stamped into the forend wood. Looks gaudy to me, but that's just my opinion. I've heard that some of the Optima's are having problems with the rib shooting loose or curling up. I think the rib is plastic and somehow the rear end is curling up on some of them. Don't mean to scare you, but that's what I've heard from reliable sources. Beretta has been pretty good about replacing the ribs, but you've got to send your gun off and wait on it to be repaired.