The throw weight requirements imposed if you want both the SCS to serve as the main bastion and range all of CONUS with many RVs are extremely high. From mid-SCS to FL is well over 14000km, even if you relax that to ranging DC or the upper southern US states from SCS it's still above 13500km. For reference the 60t D5 tops out at ~7500km with a full load of 8 Mk5s, offloading by half (~4 Mk5/8 Mk4a) only brings that to ~11000-11500km. It's just not practical to have an SLBM much larger than that, even dimensions aside such massive mass loss when each SLBM is ejected causes a sharp buoyant thrust of the sub which needs to be corrected before the next launch, stretching out salvo pacing. Assuming generally similar propellant & slightly higher weight of Chinese RVs, a D5 class or slightly larger JL-4 might be able to range most of CONUS with a mix of 4-6 heavy & light RVs from SCS, then with some missiles kept offloaded with perhaps 2-3 to range southeastern US, like how some MM3 were kept with fewer than 3 RVs during the cold war to range Central Asian targets.