10mm G40 (or 3/8" HT)
If you want a slightly stronger chain look for Maggi Aqua4 brand 10mm chain that will work as well. There might be other brands that boast higher than "standard" strengths as well.
When sizing chain you can size it "forward" or "backward." If you size it "forward" you calculate the size chain you need to hold your boat in the worst conditions you ever expect to anchor in. Amel selected 10mm chain, and this seems a good choice to me. With a good stretchy snubber, and care on selection of connecting bits 10mm chain should be fine for this boat.
Sizing an anchor "backward" is using the maximum holding power of the anchor in good conditions then using that number to figure chain size. This is how Rocna comes up with their recommendation of 11mm for a 40kg anchor.
Most cruising boat
s will oversize their anchors at least a little to help when anchored in bottoms that are less than ideal. There really is no significant benefit to increase the chain strength as well.
Fort Lauderdale, FL, USA