Do not worry you are not dreaming, just depends on the twist.
To go 1000 with a 223, you will need at the 1-8 twist to shoot the 75-80 gr bullets, and 1-7 to shoot the 90s. Some 9 twists will shoot the 75-77 gr bullets well but rarely the 80s.
AMU and USMC teams are shooting ARs with 1-6.5 and 90s at 1000 so it is being routinely done and very accurately.
I have a Savage LRPV with the 1-7, ballistically it is almost the same elevation and wind drift as my 308. Biggest problem with a 223 is spotting the trace or sometimes the impact due to smaller bullets.
Now if I was going to shoot Fclass Open, AND you reload, look at www.6mm.br.com
for the 6BR variants such as the 6BRX, 6BRDX, 6BRBG etc. good barrel life, low recoil, great accuracy etc.
If you shoot Fclass, there are two classes, the FT/R is only for 308s and 223s. If you want to shoot the OPEN class, then any caliber. Suggest you stay in the FT/R class for now with standard rifles and bipods vs full blown custom guns and rests in the Open class.
One of the major keys to LR shooting is heavy bullets for the caliber AND the correct twist for the bullet and MV. if you have the wrong twist it will not work and it will vary for a boattail versus a flatbase.
For example, in a 6 BR to shoot the 95s most go with a 9 or 10 twist and an 8 twist for the 105-107 boattails. However, I am shoot a 6BRDX with a 108 BIB flatbase bullet that needs a 1-9 twist. We have already talked about the 223s.
in 30 cals for example, Seirra lists a 1-9 twist as being required for its 240s. However, that bullet was originally designed for the AMU shooting a 300 Win mag or 30-338 Mag at 2700 fps. Take a large case mag, push the MV to 2850-2900 plus and 1-10 twist works great. Faster the MV the slower the twist can be. LR BR guys are shooting the 300 Ack Imp with 187 BIBs and 1-13 twists. My 300 WSM
Light gun shoots the 187 BIBs with a 1-12 twist at 3000 fps. Guess what, it will also shoot the 210s very well, where old school says you have to have 10 twist.