On the positive side it is accurate, probably on a par with the Swedish Mauser. The power is probably about the same as a .308. The workmanship is first rate, better than most commercial actions. I would also guess it is durable. It also uses .308 bullets unlike most European .30 calibers.
On the negative, (mine was a 31 inch rifle) they are heavy and cumbersome. I never did think the straight pull was much faster than a regular bolt action. Also the bolt face has a cut out area and does not completely cover the back of the cartridge head. This does not allow it to be loaded really hot.
When I bought mine they were cheap, then they went way up in price and I sold mine, partly because Norma was the only ammo available. They have now come back down and I would highly reccomend it mainly because of the accuracy and workmanship.
The carbine would probably handle a lot better but that really long barrel does provide a lot more energy.
I don't think that it's possible to improve on the GP-11 Swiss 7.5mm match ammo for accuracy, and the round is healthy enough to take down any North American game critter.
I picked up a primo C&R Schmidt-Rubin K-31 for $170 at a show in Reno with 99% bluing on it and superior wood. I haven't seen a nicer one yet. The Portugese ammo that I got with it was disapppointing, but the accuracy really came to life using some Ruag GP-11 match ammo I bought. It's non-corrosive, but non-reloadable.
My Schmidt-Rubin might have the best trigger out of all my rifles in the safe, and is probably only bested by a S&W Performance Center .357 revolver I've got.
Tet68, did you remove the buttplate with a screwdriver to find the orange ID tag of the last owner of your K-31? Go ahead and look under there. :)