I´m in the same boat as you.
I ordered a 1-8 and i´m going to learn to reload on it too....
We should be fine up to 220gr, but heavier bullet weights
may or may not work in our particular Barrels. It depends on the particular Barrel and the particular load. Some 1-8 will stabilize heavier bullets then 220gr and some will not. You´ll just have to try it out in your particular Barrel and Play around with some loads.
I decided on a 1-8 because it was available for me and i figured 220gr was enough for me. IF 220gr +++ loads will run, that´s icing on the cake but 220gr is pretty fine already. IMHO
Regarding super and subsonic rounds: 220gr and up are AFAIK always subsonic... you´d probably exceed the max pressure by a wide margin trying to make such a heavy bullet supersonic out of a 300 BLK.
ETA: also, let´s Keep in mind that it´s not the actual weight of the projectile that determines wether a load will run or not, it´s actually the effective lenght of the bullet that touches the grooves and lands! The weight is more of a quick and dirty rule of thumb Thing because usually, lenght and weight will correspondend with each other especially in traditional commercially available projectiles. but it´s not always the case. For instance, a semi wadcutter projectile with a short effective lenght because of the SWC design and with a boattail that wieghs 240gr will probably run fine out of your 1-8 Twist where a different 240gr projectile will/might not....
it ain´t easy.....