I guess it maybe depends on the gun and shell, but late season geese are taken much more effectively with 3.5 inch shells than 3 inch or 2.75, from my experience.
My first time using the 3.5 inch load was a few years ago. I had been shooting 3 inch and crippled two geese which swam to the middle, and had one mallard blow feathers out like he had exploded yet fly a good ways before falling. I put in the 3.5 inchers after this and I found the difference remarkable. I was stone killing the birds and a few cranes that I had been only crippling just 10 shots prior.
My patterns with the 3.5 inch are very tight. In fact, I was shooting bottles with 2.75 , 3 , and 3.5. I was dusting the bottles at a good 15 yards beyond the 3 inch.
But, if you get as good a results with your 3 inchers, then either I envy you cause you get to buy cheaper shells and get the same results, or I don't envy you, cause you're not getting the benefit of the 3.5 inchers with your gun.
Monday is the opener and I'll se if I can post some pics or videos