The 30 cal 200 gr GS is a soft point bullet with a very slightly flattened point (NOT a flat nose) with a BC very close to what a true spitzer would have (.448). On the other hand Hornady's only 30 cal, 220 gr bullet is indeed a round nose, and has a BC of only .300, much less than that of a 35 cal 225 gr partition (neither GS nor Hornady 35 cal available in ~220 gr weigt) has a BC of .430. Tell me again how that 220 gr 30 cal load performs better at distance than the .358?
And then there are no 30-06 loads with 250 gr or heavier bullets...
Comparing efficiency of loads with different powders is meaningless because you don't know the relative energy content per grain in different powders.
Well, first of all the .30 cal 200 GS is not very close in BC to a .30 cal 200 grain spitzer (.448 compared to .556). Secondly, if I was creating a heavy, distance load for the 30-06, I would be concentrating on the 200 grain spitzer. By comparison, even a 250 grain spitzer .358 slug only has a BC of .446, far behind the .30 cal 200 grain spitzer with its .556 BC (unless you don't think 25% is significant, and that with a heavier bullet that the .358 can't push as fast). For example, a 200 grain 30-06 spitzer at 2600 fps will hit with 2036 fpe at 300 yards, compared with a 250 grain .358 spitzer at 2350 fps which will hit at 300 yards with 1837 fpe, and with a 100 yard zero, the .358 will drop about a half foot more than the 30-06. Accordingly, the 30-06 will have less recoil, shoot flatter and hit with about 10% more energy. The 200 grain 30-06 load would also give greater penetration with its .301 sectional density, compared to the 250 grain .358 sectional density of .279
As to the 30-06 having no loads with the 250 grain bullet, I don't buy factory ammo anyway. If I want a 250 grain bullet, I'll simply load some. In fact, I have an old Shooting Times issue with a 250 grain 30-06 load producing about 2450 fps.
Finally, as to comparing loads with different powders, I merely took the top load for each and compared weight of powder. If you are wanting to talk efficiency, it would seem that you want to know how much powder to achieve the desired results, regardless of which particular powder works best for either cartridge.