I'm 6'5" and about 290 lbs...( just you're average sized Buffalo ...)....so yes, I might be in a minority among bird hunters...for upland birds...with an 8 lb Over Under...But seriously - my gun choice / and gague will depend on a lot of things:
If I'm in open country / fairly flat and easy walking ...and good dogs...hunting with an 8 lb gun is no big deal. If I'm in a hunting party - where I'm only the hot gun on every other flush / or every 3rd flush / or watching the dogs and letting younger guys shoot most of the time ...its easy, in open country, to break the gun and carry it over my shoulder or in the crook of my elbow.
If I'm stepping over sugar beet rows all day long...and with a gun at "port arms" all day long - yes, 8 lbs gets too heavy - and wears out these old shoulders../ or in brushy areas....8 lbs is a little too much as well...
I have a lot of guns so I have options... in a semi-auto I can go to a Benelli super sport 12ga 30" barrel is only 7.2 lbs ....or in a 20ga version with 28" barrel its only 6.2 lbs ...( and either gun gives me the 3rd shell too ). Both good guns / good options...
My primary O/U's are all the same 30" barrels, Citroi XS Skeet models ( but the 20ga, 28ga and .410's were all built on the 20ga receiver..) so in their original configuration they're 7 lb guns.....for competition / to smooth the swings out - I put 8 oz of lead tape under the forend...and 8oz in the stock hole..(being careful to tape them in - to keep the balance at the same point ) and I raise those 3 guns to 8 lbs....but I can just as easily ( in 10 min ) remove the extra weight and shoot them as 7 lb guns as well...
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But like the OP is leaning ...toward one gun / maybe the Citori 725 series...that gun, at least right now, 725 Field ...is only available in 26" or 28" barrels and is a 7 lb gun ...and I think he said something like 5'7" and 165 lbs...maybe that gun in a 28" will be perfect for him / where I might find it too light to be an "optimal" gun for me....
When he's in his 60's like I am ...maybe he'll have 6 or 8 guns to choose from ...and pick one for each trip that suits him.
Guys on the forum - that know me --- know I like longer and heavier guns...heck for Trap, my primary O/U is a Citori XT with 32" barrels that weighs close to 10 lbs...( my shooting buddy refers to it as a "sewer pipe" ...and says he'd need a tripod to shoot it "...) ...but at the same time his primar Skeet gun is a Krieghoff K-80 with 28" barrels at about 9.25 lbs...and he's only 5'10" and maybe 175 lbs...( just a little fella ) ....and closer to 70 than I am too ...