Even with the velocity you'll get with the 6-284 you may not be able to stabilize the 115's with an 8 twist. I tried them in a Lilja 8 twist from a 6-06 and couldn't make round holes at 100 and 300 was even worse. RL-25, H1000 and Retumbo all made good velocity but I ended up shooting the 107 SMK's with H1000 which shot in the mid .3's.
Of the powders i tried H1000 did better than anything else with the 115's.
My Broughton 8 twist 243 Ackley loves the 115's with RL25. FWIW