Nice guns, but after owning nearly 20 of them, here's some observations:
The older guns (pre serial number) have a thinner stock and forearm and feel more sleek than the newer ones. Generally, the newer guns are made of a cheaper hardwood (beech or birch), but have better bluing. That said, I've had newer ones with some nice oil stained wood. These were most liketly the wood used on the "Fox model B", which was simply a 311 with nicer features. The bluing on some the older ones though had more of a "painted on" bluing and I've seen this flake off.
The case color on the older guns tend to get spotty rust pretty easily. Fixing the case color is fairly easy with cold blue and a torch if you know how to do it. The later newer guns had a blued receiver, more of like a duracoat. I have a 410 like that.
All the 311's tend to crack in the wrist area. These were guns meant to be used and many were put away wet, then left to dry in the corner of the closet.
The 410's go for quite a bit of money, I've seen them for $600+ for nice ones. I sold my 311R awhile back for I think $550. I could have sold that gun many times over for that price. The 26" barrels in 12 and 20 gauge seem to be a bit more uncommon. all the 311's tended to be choked real tight, and with todays modern ammo they tend to pattern very tight. Handloading or opening up the chokes solve this problem. I have an older 20 gauge that is a bit more open than I/M, and I've been told this is quite uncommon. The gunsmith says it does not look like the chokes have been opened either.
That's pretty much what I know about these off the top of my head, but Okie seems to know quite a bit too.