Between the two spring choices you have, use the 11# spring. I tested 10, 11, 13 and 16# (stock) and the 10# gave me the fastest reacquiring of the target. I’m shooting my reloads which consist of 124 Gr FMJ truncated cone from RMR with 4.2 Gr of Winchester 231 @ 1.102 OAL.
Edit.
I’m also using the stock thin buffer that came with my TSO.