I have chased the 129gr SSTs around. Just shot a trial last night. Homing in on ~45.5 RL-19, 20 thou off the lands in my 260 Rem. Despite sending a lot of SSTs down range at paper, I have only shot one buck so far with the 129gr SSTs. Have also used 129gr SP Interlock with N165 (46.3gr). These flat based bullets shot very well in the last 260 Rem again at ~20 thou off the lands and show promise in the new one.
In the Hornady book, RL-15 shows lower max velocity than 5 others (IMR 4831, RL-19, RL-22, H 4831, Viht N-165). Somebody muttered about RL-17 earlier in week as an option, but I am trying to ignore that one at present.