I can tell you that the 60" pin on bucket on my L3200 holds 1/4 yard per scoop when I get a good heaped scoop (which doesn't always happen unless the pile is big and easy to push into). That would be the same 60" pin on bucket the L3800 gets.
I think the optional SSQA bucket is 66", so it would hold marginally more (as long as it's not a light materials bucket, in which case you're not supposed to load it all the way up for heavy stuff).