For some scopes, the best clarity is in the middle of the elevation adjustment.
Will you dial vs hold for elevation and be in the middle of the adjustment range more often than not? If so, get a 20 MOA mount. If not, don't get a canted mount. But consider this...
You will use about 2.5 MOA just to zero the scope. You will use at most a bit over 4 MOA at 300y and around 16 MOA at 600 yards with a 100 yard zero.
So a 20 MOA will be ideal for 600y and up. A 10 MOA mount will be ideal for 300y and up.
You will be getting close to 30 MOA at 800.
A long range 30mm tubed scope of 5-25×50 will probably have a bit over 30 MOA of adjustment in each direction. A 34mm tube will eliminate the NEED for a canted base because of the extra elevation travel.
You WILL NEED the canted base for shooting past 800y with a .223 rifle and 30mm tube. Though, the ability of a .223 to shoot past 800y is dubious because it will become subsonic and suffer transonic accuracy issues.
For .223 I would get 0 MOA or 10 MOA of cant.