26" Barrel, RL26 works great in cartridges like 6.5 Creed or other 6.5 with similar case fills, 243 gets an extra 100 fps with it as well.
Take for example the 280ai, the loads are based on QL, there is a 280 win load listed at Berger bullets Max of 56.4 gr RL26 with Coal of 3.367" using the Berger 175 gr Elite hunter with vel of 2773 fps, QL shows same load producing 2778 fps and the 175 ELD-X getting 2826. So I would say that QL is probably close as well with their data on a case with 6 grain greater Capacity.
Are you talking about 178 ELD .308 bullets? If you are using 43.9 gr of Varget it is getting towards or over max depending on your Case and COAL.
RL26 would be way to slow for a .308 case and 178 gr bullet.