I too have a Classic 36, and currently have 75m of 10mm ISO grade 4 chain, attached to a further 25 of octoplait.
When I bought the boat it only had 25m and as I am in the med you need more. We spend 50/50 of our time at anchor or stern to a quay so you need a fair old bit of chain. So I added 25m using the chain links from Jimmy Green, then added a further 25m. This winter I am replacing the original 25m that were supplied 21 years ago with the boat, as they are rusting, so we will still have 75m.
As for the weight issue, my boat seems high in the water at the bow in any case. Also I tend not to fill the front water tank which holding 160ltr more than offsets the extra weight.
I have also just replaced our original Brittany with a Manson Supreme. The Brittany was great for us, its only down side is I believe you need to lay out around 10 to 15m more chain than everyone else as the pull on it needs to be horizontal. I am hoping for the same holding with the Manson but using slightly less chain. We shall see.