Kmfl, I have a similar set-up- 8x8x22- that I split into 3 rooms, two are 8x8x8 with a 4x8x8 store room between them. 4000 wtts in the flower room, floro's for the veg. room.
I veg till they are at least 2ft, sometimes taller( 2 months vegging at least). Depending on strain and technique, they will be from 30 inches to 60-70 inches by harvest. I have a total of 18 in the flower room and sometimes it gets CROWDED!! Take it for what its worth, thats my 2 cents.