www.benelliusa.com
The Benelli website shows a model #10818 Montefeltro Silver Featherweight 12ga with a 26” barrel. I looked at 4-5 online gun shops and they do show it in a 26”. However, they were all out of stock although a couple will back order for you.
The 28” will give you a longer sight radius which is generally thought of as an advantage is some cases. That’s why there are 30” and 32” trap guns.
The 2” difference shouldn’t affect balance much but as you say the 26” may handle a bit quicker to the bird. The old quail gun duck gun difference.
The 28” is a bit more cumbersome in and out of the pickup seats if you travel with guns inside.
The 12ga 28” Silver is 49.5” overall. My SKB O/U with 28” barrels is 44.5”. So it would appear the semi-auto action adds about 3” compared to an O/U; I’ve never felt my O/U sight radius was too short. Personally in a S/A, I’d prefer the 26” too. Even a 24” would work for me.
I’d back order and get what I wanted if it were me.