In Australia, the only chain recommended for anchoring boats is a tested short-link chain called Grade L, and it has the letter L stamped on every link.  A lot of people here use cheaper Chinese chain that is not tested but I don't trust it. 

I am an empirical seaman, couldn't quote engineering specs to save my life, but I just look, read and talk to experienced sailors to learn what to do, with anchoring and everything else.  As I understand it, anchoring is different to suspending your boat from a chain (its lift strength).  The boat is afloat and the forces on the chain are quite different.  The biggest risk is snatching loads, which is why I always tie a 3m nylon rope to the chain once the anchor is set and I have enough scope out, then veer some more chain until the nylon snubber is taking the load and the chain is hanging in a loop.  That way the nylon absorbs the load.  If you have plenty of chain out it is also hanging down and it takes some force to lift it up until it it stretched out straight, as well as putting a horizontal load on your anchor (catenary).  This absorbs a great deal of the load.  Eric and Susan Hiscock's primary anchoring system aboard Wanderer 111 used 80 metres of 8mm chain, attached to a 35 lb CQR anchor.  They also used a 10 kilo weight on a traveller to slide down the chain if they thought it needed more catenary.  They were deeply conservative sailors and sailed more than twice around the world with this set up, 110,000 ocean miles in total.

I have done a bit more research.  I found that Rocna recommend 8mm chain for a storm anchor for a boat of Gecko's size, though a chain of higher specification than I looked at when I came up with 12mm.  Still, going backwards from the safe working load of the specified chain to the expected load, it's less than half of what I got from the Complete Anchoring Handbook, and a little below just the wind load at 60kn quoted in there.

Still, I guess a better grade of 8mm chain is a better choice than a basic grade and 12mm.

So I searched for better chain in Norway.  If a web site said anything at all, I found no reference to grade 40 or high test chain, or to grade 70 or transport chain, only to DIN 766.  I could not find the specifications for that norm, so I have no idea whether it says anything about mechanical strength, or whether it is limited to specifying the dimensions, so that the chain fits onto a windlass.  I have found an Italian supplier for grade 70 chain.

Ruffles Spray has had a Rocna 34kg anchor since 2006, it's attached to 100 meters of 10mm chain, Ruffles Spray displaces 20 metric tons. We have had winds of up to 100  knots and have never had any problems with this setup. 

Arion displaces about 5 tons and I use 8mm short-link tested chain as my main anchor rode, with a nylon snubber to absorb shock loads, attached to a 15 kg Rocna anchor.  As long as you have plenty of scope (3 to 1 in very deep water, up to 10 to 1 in shallow water),  you will never part it.  I have dragged a couple of times in gale-force winds when the bottom proved unstable but have ridden out two cyclones with winds over 80 knots in sheltered bays with a good mud bottom.  On both occasions the boat was getting knocked down in the gusts but the anchor and chain gave no trouble.

I'd take that with a pinch of salt. Rocna vs Manson has been discussed to death on the ybw fora (aka the anchor wars). Interestingly Rocna themselves had quite a quality problem after moving production to China but that seems to have been sorted by now. Both are very good anchors and certainly an improvement over ye olde coastal quick. The first thing I ever added to Tin Hau was a German Buegel anchor,the original roll bar design (beware off cheap knock offs though!)