@rjb The distances you cover would likely put you in an extreme group whatever the lube you were using.
For me, with two chains, I always have one on the bike and one clean, because its very easy to cook several chains in one go. For me 200-300km works out to a chain rotation every 2 weeks. I always put a freshly cooked chain on before I go Audaxing as that's part of the pre ride fettling.
The maximum distance I've gone on a single waxing so far is about 400km. At that stage there was nothing telling me that I urgently needed to rewax the chain so it could be that I am being excessively conservative in my rewaxing schedule.
For wet rides you have to consider that the outside of the chain is covered with a very thin non-sticky coating of wax, so basically if the chain is muddy, just slushing some water over it would be perfectly fine and would wash off the loosely adhered crud. My advantage here is the single speed chainline, I don't have deraillierus and cages to collect crud and spread it around.
When I rub my hand up and down the chain before I remove it for rewaxing, my hand comes away effectively clean, just some slight smudges for loose wax flakes.