Our .308 cal. 175 gr BD2 bullet has a BC equivalent to the 140gr Berger, and I think can be launched at the same speed. As far as the most efficient.264 bullet Hornady makes a 153 gr .264 bullet with a G7 BC of 0.358 and we make a 135 gr .264 BD2 copper bullet with a G7 BC also of 0.358, so in terms of BC/grain the 135 gr BD2 bullet would be the most efficient. Look at the posts above. We are going to try and see how well our heavier .308 bullets with higher BCs will perform from a 24" .308 Win. The Hodgdon Annual Manual for 2022 suggests that CFE223 has the best speed for a 200 gr AFrame at 2580 fps, so propelling our 195 gr BD2 bullet with a G7 of 0.347 would at that speed would not be unreasonable to try. You are probably correct that we may not be able to equal the 135gr .264 SBD2 in the Creed, but with the tricks discussed above for the 308 Win we may be able to equal it using our 205 gr SBD2.308 bullet. We will have to see.