Its roughly a 2" overall length difference between a semi-auto or pump and an Over Under..with the same barrel length .../ ...so a pump or semi auto with a 28" barrel is roughly the same overall length as an Over Under with a 30" barrel.
Today... 30" barrels on Over Unders are more common on Skeet and Sporting Clays fields .... 32" Over Unders are more common on Trap fields....( 26" Over Unders were common for a long time on Skeet fields...then it was more common to see 28" and about 15 yrs ago it became 30" barrels...and for 4 or 5 years some shooters tried 32" barrels and most of them dropped back to 30" for a general purpose shotgun for Skeet and Sporting Clays.
Its not so much barrel length ...as its the overall weight and balance of a gun that matters....to me 30" O/U in a gun that weighs about 8 1/2 lbs is perfect...but I'm 6' 5" and 290 lbs../ my buddy is 5' 10 and 160 lbs soaking wet, he thinks a 30" gun feels way too long and clumsy...so he has stayed with a 28" and a little heavier at around 9 lbs.../ but it depends on you and your experience.
There is no -- one right answer...but in general, for most shooters, a 32" O/U is a little too long ...for a general purpose gun for Skeet and Sporting Clays.
Now, if I were to go to a real light gun...around 7 lbs...( like a Benelli Super Sport 12ga...I like it in a 30" barrel ..)../ so its about the same overall length as an O/U with 32" barrels....) ..but I like it in a 30" barrel, because its so light, that it tends to be "whippy"...and the extra barrel length helps me smooth out the swing on follow thru ...its a nice all around gun../ but I still tend to add weight to it ( with lead golf club tape ) I add 8 oz in the butt and 8 oz under the forend...to get it up around 8 lbs...
Besides the Benelli Super Sport 12ga ..( semi auto with a 30" barrel ) ...which I use primarily as an "all weather gun" or as a "travel gun" where one gun will do most everything pretty well. I still rely on my primary guns, to be Over Unders, Browning XS Skeet models at around 8 1/2 lbs and 30" barrels...in .410 / 28ga / 20ga and 12ga..( the .410 -- 28ga and 20ga --- were all made on the 20ga receiver so they are lighter right out of the box at around 7 1/2 lbs, so I add 8 oz in stock and 8oz under forend...so all three of those guns, swing like my 12ga version in the same model ).
I have one O/U in 32" but its a Trap gun...Browning XT Trap..and it weighs up around 10 lbs....its way to heavy and clumsy for Skeet and Sporting Clays. But the weight and extra length for Trap makes it perfect...because Trap birds have way less left to right ...or right to left movement...so the extra length and weight on a Trap gun helps keep the momentum up, creating a smooth follow thru on trap.../ but to stop that swing...and come back hard the opposite direction after a crossing target is too much for me. I can do it for giggles...but my scores go down...
