I don't have a .300 RUM, but if I were choosing between the two loads you mentioned, I'd go with the 165gr Partition over the 150gr Accubond. Big, overbore cases like the RUM are going to be more efficient with heavier bullets, and the partition will hold together better if you shoot a deer at close range where impact velocities are very high. The Accubond shouldn't blow up on impact, though. If I had a .300 RUM myself, I'd shoot 180gr bullets for everything, and my bullet of choice would be either the Barnes Tipped TSX or the MRX.

Mike