My thoughts:

• Hitting the 3 seems overly risky as I can't make the point in the near future and it doesn't help me much in the race.
• Playing 14/9 sort of sucks as it leaves two direct shots on an advanced blot.
• Playing 15/8 sort of sucks because it creates a big stack that doesn't help me with my diversification problem.

Eliminating all of those 5's left me with final move.

1. XG Roller++ 21/20 8/3* eq:-0.111
Player: 46.89% (G:10.69% B:0.38%)
Opponent: 53.11% (G:12.18% B:0.27%)

2. XG Roller++ 8/3* 3/2 eq:-0.119 (-0.008)
Player: 46.85% (G:11.62% B:0.39%)
Opponent: 53.15% (G:13.79% B:0.38%)

3. XG Roller++ 14/13 8/3* eq:-0.123 (-0.012)
Player: 46.66% (G:11.11% B:0.38%)
Opponent: 53.34% (G:13.33% B:0.31%)

4. XG Roller++ 14/8 eq:-0.146 (-0.035)
Player: 45.61% (G:10.08% B:0.34%)
Opponent: 54.39% (G:10.94% B:0.21%)

5. XG Roller++ 21/15 eq:-0.147 (-0.036)
Player: 45.52% (G:9.32% B:0.37%)
Opponent: 54.48% (G:10.62% B:0.22%)


So, it's a super close play with a lot of variations. I am not sure how large of an equity difference is required before a play becomes an "error", but I posted this because I was very surprised that hitting is the clear play here and that it doesn't matter much what you do with the one after that.

I played 21/15... woops.

The value in hitting is probably the fact that even if it "goes bad", getting hit means you have a return shot. You're far behind in the race, have more men back, and have a stronger board than your opponent, so Magriel's Bold-Safe criteria points clearly to hitting. You'd like to start an exchange of hits to possibly change the momentum of things. The status-quo is not good for you.

I had come up with 8/3*, 14/13 before seeing the rollout.