Is there any advantage to all chain?
Oh no!! This is one of those topics where opinions abound.
The best thing to do, on such common topics, is to use the search function. You will get a lot more information in a lot less time. Anchors and chains have been flogged to death.
AYBC recomends 2400 pounds working stength for a 40' monohull, though for durability most sailors go up one size, inspite of the fact that the AYBC guidline is already conservative. Thus, 5/16" G4 is a common suggestion. 1/4" G70 would meet the requirement, but is a more unusual choise.
There are 3 reasons for all chain:
1. won't cut
2. feeds through the windlass better (the rope/chain splice can be a problem)
3. the weight helps the anchor wet and helps it stay
The down sides are:
3. less shock absorption, specifically in shallower water (a long snubber can solve this)
I've used both and favor ~ 100 feet of chain backed by rope for my boat, but it will be a long discusion.