I never said the .243 was a bad choice lol, i do think it's a great cartridge, but in today's choices and general understanding of ballistics there are some fantastic other choices too.
To make a .243 sing like you're describing then you have to rebarrel to a 7 or 8 twist, you have to reload 105-115 gr, maybe have magazine length work done on the rifle to handle the out of spec oal of the new round etc. etc. etc. bla bla bla
Love to see a factory .243 shooting factory ammo even get to 1100 yards supersonic.
6 creedmoor or 6.5 creedmoor will do that, factory rifles/ammo
the OP didn't specify his level of tech around the .243 question, assumption is he was inquiring about saami spec off the shelf .243...peace bro