For what it's worth, I just had the same dilemma on my Hylas 46. I only had 145 feet of 3/8" BBB chain with a 44 lb Rocna. I talked with Bob Pingel a bit and he noted that John Kretschmer switched to 5/16" G4 for his Kaufman 47. And it's a heavier boat than the Hylas 46. So, I figured if that was good enough for John and all his passages, it was good enough for me. I decided on 300 feet of 5/16" G4 and switched to a 55 lb Rocna. 300 feet gives you a 10:1 ratio in 25 feet of water (assuming 5 feet of freeboard). The selling factor in going with 5/16" was weight. 300 feet of 3/8" is 175 lbs heavier than 300 feet of 5/16". That's a significant weight reduction in the bow. The 5/16" G4 also has a higher working load limit than 3/8" BBB. So, compared to what I had before, I was getting a higher working strength as well. Of course, you'd need to purchase a new chainwheel, but it's easy to switch out.
Chris
s/v Seven Iron