My Gas rigger really Likes the V967/3, ( full mod 260 tho)( My 230 mod spun it as well.) with 5.8 pitch. So 6.4 would be a good starting point for the 231.
For more speed 2170 moded.
The V967 I take a 1/8 inch off starting at the hub to 0 at the tip.
Recup to 6.6.
I have 3 different moded 2170s and they all act different.
2 are brown props, they work really well.
I have tried others, but always am back to the 2 listed.