Opinions are like noses, everybody has one... that said, I'm gonna take some exception with the previous poster and will pass along my own EXPERIENCE.
I looked for about a year at 91/30's not so much to make the perfect purchase, but more of a shopping experience. I saw low end's (rough condition wise) and High ends (really pretty). Now I am a history buff, so I also started reading about the rifle in battle conditions. So that's my background. I also wanted something that was not just a wall hanger, but something that could put bambi's Pappa in the freezer. Prices can be outrageous on both ends. Original sniper models can fetch 5-700 bucks, maybe more with the PU scope. Unless you are a collector, I would steer clear of these. I just wanted a basic model, not too dinged up. Prices were running from 90 - 200 bucks for these. Finnish models are highly sought after since they were better made. Visit this link for everything you ever wanted to know about Mosins:
http://www.mosinnagant.net/i3tro4.asp
One fine day all the pre-conditions came together (Gun slush fund at +200 bucks, nice example in a stores consignment rack, ready to buy feeling). The example I picked up had the ATI scope mount/bolt already attached - no Scope, but the price was 100 bucks.
It had all matching serial numbers, (Look on the butt plate, the bottom of the receiver, and the barrel), and MOST importantly very nice rifle'ing when viewd with my pocket penlight. The barrel was black, but the grooves stood out.
The stock was full of cosmoline, I'm guessing it was gunked on and wrapped in freezer wrap paper for about 50 years before winding up in my hands. Still for a hundred bucks what does one expect. It took me quite a while to get the stock to MY desired finish. Many will think this sacreligious, but its my gun... I used several rags, and gasoline out in the back yard to completely remove all finish and all the cosmoline. I then smoothed out dings using a hair dryer, and 800 sand paper. I was careful not to remove any of the arsenal markings. I took the stock to a woodworking guru and looking at the colour under the top of the forearm, (it was somewhat a cherry color) I combined two stains, a dark walnut and a cherry to come up with the color I wanted. Initially, it was too red, but some darker mix of walnut corrected that. I finished the stock off with an oil finish.
Next I turned to the barrel. This too was a multi week process going through several levels of grit cleaners always rotating in the direction of the groove. The next to last step was to "Cork" the barrel. This involves 3 very thin slices of cork taken lengthwise from a wine bottle cork. One piece goes over the top, the other two support the bottom 2 thirds of the barrel, and they go under the barrel up at the front most band.
Prior to this "corking", bench shooting at a local range with a target at 100 yards produced a pattern about the size of a small coffee cup saucer. Once completed, the pattern was reduced to the size of a small expresso coffee cup. Attaching the bayonett moved the entire pattern down and right.
I mounted a Wally World 125$ scope on my 91/30, and for the price it is fantastic. Ammo 7.62x54r is inexpensive especially when considering just how powerful a round it is. I now keep several tins of it and watch for any discount deals at gun shows.
OK so I've passed along my little story and with respect to your questions,
1. Hex or round - only difference is one's older (what looks better to you)
2. Arsenal marks - Just means some slub in a commie factory took everything apart put
it back together and shoved it out the door. I would look to see a clean (Non
counterbored ) muzzle... Really look for solid rifle'ing
3. Laminated vs non ( do you like Blondes or Redheads?) just a preference thing
Here's what I take to the range, and it never goes that someone admires it and asks about it.
Tips,
Make up and attachment that will screw on the rifle's cleaning rod and swap out with a damp cloth (I use windex, but any commercial cleaner will do) I then do a thorough clean once I return home.
Cork the barrel, it will improve accuracy.
Shoot the beeejeezus out of it, it was inexpensive to purchase, and you can taylor it to your own satisfaction.
Watch out cuz once you buy one, a penchant for more develops, I now own 3.
KKKKFL