The 243 is gonna have less recoil. If you have a fast enough twist barrel u should be able to shoot 105 begers around 3000. That would be plenty. But with the 6.5 creed your heavier bullets will buck the wind better. That being said I would probably go with the creed because I would like to have one myself.
I own a Creedmoor and shoot 140 Bergers at 2825 fps; my shooting partner has a 243 AI and shoots 105's at over 3100 fps. At all ranges inside 1200 yards (I haven't shot further when with him) his rifle shoots flatter and it's rare that he has to really add any additional wind adjustments compared to me.
I like my Creedmoor a little bit better from a dual purpose standpoint because almost 50% more bullet weight never hurts when you hit flesh. From a strict target perspective he's got me convinced to build a 6mm or some sort in the near future. The recoil is less than my 6.5, bullets are a little cheaper, and they're just plain fun. In my mind you can't really go wrong with either.
I have a 243 win with 26 inch 1/7 twist barrel that I'm getting a bit over 3100 fps with berger 105 and 115 vld hunting bullets. Have no problem going to 1000 yards with either one, I did pop a coyote at 1,237 about a month ago with the 115 grain. I went to the 243 from a 300 win mag because of recoil. Two years ago I took a whitetail buck that measured 163 and change at 548 yards with a 105 gr a-max, rib cage in and out and you could have put a baseball through the exit, lungs were mush and he flopped in 20 yards.
If you look into the competition realm, the 308 died at the hands of the of the 6.5. Now i'm starting to notice (not that I pay a lot of attention to it) a good number of 6mm's running the course.
Why? Speed. A 243 can get a lot closer to the "usual" limit of 3150fps for match use. Speed makes a flat trajectory, a flat trajectory it easier on the end user when a distant target is misjudged.
Why use a 6.5? More energy means a close miss at ELR distance is usually easier to spot. A larger bore to case capacity mean the throat is going to last longer. The 6.5 is known to have excellent BC which is going to buck the wind better when velocity starts to drop.
If you ever decide to take your new rig hunting, the 6.5 will give you a little more room for error. Having said that, i've killed more critters with a lowly .243 than most of my rifles combined; it's the indian, not the arrow.
I have both & love them dearly. For my preference, I rock my Creedmoor most of the time. In the grand scheme of things, you cannot go wrong either way.
I've been using a 243 in competition since 2013 and have gone through three different barrels, two of them in 2013 alone. I'm pretty familiar with this round and have been using the AI version since the beginning of 2014. Accurate barrel life in a competition rifle isn't that great, I'm getting at most 1400 rounds before velocity has dropped way off (150 fps) and getting erratic uncalled fliers. I'd urge you to look into barrel life of the 6.5 Creedmore. From what I've been hearing, it is getting over double what I see in the .243 barrel. Ballistically, it's a toss up and I've deflated several critters out to 500 with the .243 and 105 hunting VLD's, but agree that more weight behind the bullet is a good thing.