With a 1:8 twist you will be able to shoot any bullet weight, up to 77 grains, that will fit in a magazine. Most mags won't take more than 2.270 to 2.275 OAL cartridges and most 80 grain and higher bullet weights have longer recommended OALs than that.
With a 1:7 twist, you can shoot heavier bullets than 77 grains but you would be wise to consider shooting with a single shot adapter if you have a magazine.
Also check the bolt action before you consider single shot loading. A push feed bolt instead of a controlled feed bolt would have a better chance of feeding a single round placed on top of the mag.
My CZ .223 has a Mauser-like controlled feed bolt and prefers to pick up the rim up from the mag. With a long cartridge, my mags won't take a cartridge over about 2.275 OAL. When you place a longer cartridge on top of the magazine using a controlled feed action for a single cartridge placed on top of the mag, the ejector doesn't always click over the rim as the cartridge feeds. There is a single shot adapter for a CZ that seems to work, but CZ doesn't sell 1:8 or faster twist barrels. They only sell 1:12 and 1:9 so using single shot loads with really long OALs doesn't matter much unless you are trying to minimize the jump to the rifling like I was doing.
If you want to shoot bullets of 80 or 90 grains with a 1:7, you might want to consider single shot TC rifles, assuming you can get one with a 1:7 twist, since they don't have a bolt feed mechanism to fight with.