My trick for using Opus is using it exclusively as a subagent managed by Fable.
"Use Opus subagents for this work where possible" is all it takes generally.
In my experience Astra/Sol are both quite good as workhorses, but not at Fable's level. I use them every day very successfully and I'm very picky.
I used to do this but recently I switched to having Fable 5.1 spawn forks of itself rather than Opus subagents. Yes it's more expensive but you don't pay for reads that already happened pre-fork, and you end up doing less rework since Fable agents are just much smarter.
Quite good as work horses? To me Luna is the work horse and Sol and Astra are prancing thoroughbreds. If I use Sol or Astra for anything other than curated reasoning and planning I will burn through my usage limits in an hour.