Well, you can run the figures all you want, BC, SD etc. of both the .243 and the 25-06, and come to some conclusion that the .243 will outperform the 25-06. Field results are where it counts. If your .243 works well for you, then by all means use it. I prefer my 25-06. If you wish to shoot 117 gr. bullets in the 25-06, then go for it. 100's work great for me.
I can just as easily use my .243 (two of them) or my 6mm06, but when it comes to antelope my first thoughts are 25-06. I like it, the rifle fits me well, it's accurate and a real pleasure to shoot. I have confidence in it based on in-field experiences. The Speer 100 gr. puts them on the ground, 7 of them so far with that rifle / cartridge / load and none lost with shots up to 300 yards. The Speer is a bit tougher constructed bullet than a lot of 100s are. I have taken mule deer too with that load. Are you suggesting that I should switch to my .243 and 100 bullets because the BC and SD aren't right?
I could just as easily load heavier bullets. I have some Nosler 110 gr. Accubonds, Hornady 117 BTSP, and some Sierra 117 gr. Spitzers on hand. When load developing, the Speer 100s turned in the best accuracy. I gave them a try. They work well in the field for me, so I have no need to switch. Actually that bullets works so well and is so accurate in my rifle, that is is now my bullet of choice for deer, antelope and on down WHEN I use the 25-06. The same load is a great groundhog getter, crows too. What ever works, works, right. The BC, SD figures are so slight as to be negligible in my mind. There is one other consideration, however that hasn't been mentioned, and that is bullet diameter.
Maybe if I were shooting extended ranges, I might consider a heavier bullet in the 25-06, but only if I could get the required accuracy to be able to pull off a killing shot. But, when I think of ranges further than 300 yards, I generally step up to a larger caliber, generally a 7mm. I wouldn't reach for a .243. But hey, that's just me.
The 25-06 is a great cartridge any way you look at it.
Enjoy your rifles / cartridges whatever you use.
Just out of curiosity, how many of you are using a .243 and 100 gr. bullets for antelope? I'd like to hear your successes, and some good photos of course. Not that you are going to talk me out of my 25-06 and the Speer 100s, I'd just like to hear your stories and learn.