"besides the look.. and the "sturdy feel" of a built in.. what else is different besides built in and free standing ones."

You just answered your own question. If you aren't up on what the differences are, then you'll never notice which kind you have once it's installed. And no, built ins are smaller on the inside than a "regular" fridge because the box is smaller. I wouldn't categorize them as having a sturdy feel either.

boxta - Our two Sub Zeros were installed in 1987 when we renovated the house and enlarged the kitchen. When the time comes to replace them we'll have to confront the same problem. Since I want to be ready for that day and not be forced to make a quick decision that I might be unhappy with later I called a cabinetmaker to check and let me know what was possible.

We do have a small cabinet above both the freezer and refrigerator and above that is a soffit. The cabinet maker said he'd be able to remove the cabinets without altering the soffit which would allow enough space for the taller Sub Zeros. Since our cabinets were custom we asked our original contractor to make sure we had plenty of leftover trim and panels just in case of a future remodeling.

If you're still interested in a built in then I'd suggest you call a contractor or cabinet maker and have them look to see if it's feasible and get an estimate. That just might help you decide.

Liebherr has their 36" FD in an 80" height. In fact the 84" version is still the same 80" compartment with doors that are 4" taller. Could that fit your 76" opening with less modification?

2010 cabinets are probably still in production. Usually the cabs above a frig are deeper than others and are installed with several screws that can be removed. The manufacturer or local rep can match your finish on the pieces needed for your new install. The sz site has fab and install info.