I think you might want to look for a little larger caliber rifle for long range (1,000). Most long range beginners and even alot of experienced folks prefer the .308 Win. B/c the large projectile is heavier and has a higher ballistic coefficient, or BC. Also, the larger heavier bullets are not quite as affected by wind and other elements.
If you can master the .223 @ 1000,I think you'll be alright for other calibers.
It's not gonna be easy, but don't give up. I know most people consider the effective range of a .223/5.56x45 to be 600 meters, as far as lethality goes. But there's guys shooting them at 1000 for killing paper and possibly small varmints.
If you decided to go with a .308 or 6.5 Creedmoore, or something like that, all you'd have to do is rebarrel your current rifle and put a different bolt in it, with a larger bolt face, (.308 is considered standard bolt-face for SA rifles).
Either way, good luck man, and let us know how it works out for you.