I had good luck with the 300gr FTX in the 54cal. Its a little on the tough side. I think the jacket might be thicker than the 45cal FTXs/SSTs but im not sure. It should be a good candidate for sabotless especially with the nice engraving you are getting.

The Rem 385gr seemed to be even tougher. I actually wanted to build a Rem700ML with a longer 54cal barrel to ring the most out of this bullet. It has a good BC for its weight/caliber but recoil is too harsh in my 54-120. The extra weight might help getting a more efficient burn with BH209 and sabotless. Tom Post got a 350gr 458 shooting nearly 2000fps with 120gr of BH209 but that was in a 45cal.