Start by looking at ...and understanding the adjustment issues and options in a gun like the Benelli Super Sport ( not the Sport II model ) ...
The super sport is a carbon fibre gun ....with shims ...changeable comb pads...changeable butt pads...comes with 5 chokes...has the "comfort tech" recoil supression system in it... 12ga comes in 28" or 30" barrels ...its a really light gun at around 7.2 lbs ...inertia operated so it shoots clean ... Downside on it is list price of $ 2,069 but in my area its selling new for around $ 1,875 ...but my point is, understand the adjustability ...
and then look at other models of guns ...some with similar options ...some with no adjustabilty ...
and figure out your budget ...and how you want to make a selection..
There are guns like the old Remington 1100 ...and a company Jack West stocks ...that makes a parallel comb synthetic stock - with an adj comb insert - and a soft comb insert for the 1100's and the 11-87's ( and the 870 pumps) ....and while the 1100 is old technology / understand the adjustment issues ...so a gun can be made to "Fit" a shooter... The Jack West Stocks ...in my opinion ...take an old technology gun ...and make it a very very good gun with a lot of adjustability.
and go to a club - talk to a lot of serious competition shooters ...and discuss fit / and guns / and durabilty ...and shells ( 1 oz, 7/8 oz in 12 ga ) and velocity ...and chokes ...and whatever ...and find out what they doing / and why !
http://www.benelliusa.com/shotguns/benelli_supersport_and_sport_2.php
I'm trying not to say ....buy a super sport ..and you're all done ...you have to do what is best for you ! There are a lot of good guns out there / they're just different ...and priced to meet certain price points ...options cost money ...do you need them ( maybe ) ...maybe not.
Today I'm 6'5" and 275 lbs ...but my weight tends to flucuate ...so I will sometimes adjust my combs mid season .../ and I need guns that have a comb parallel to the rib ...so I can shoot the same gun in a T shirt vs a heavy coat and vest ...without Point of Impact changing .../ most all of the semi-autos do not have parallel combs ...but just because I find that the most versatile / doesn't mean you will.
It just isn't as easy as ....buy the Browning Maxus, or buy the Benelli Super Sport ....there is a lot more to it.../ and no matter what - have fun with the process !