Sounds like a similar set up to ours except your on a lot larger scale! Who says it all has to be one system? We used to calve 120 cows but have dropped that back to 80 and now buy in 30-40 suck calfs (230-300kg) in September/October and buy some stronger store hefiers to finish in the shed over the summer to make use of shed space it seems better for us as cash flow is better and spreads the pressure on grassland. We graze the store hefiers graze the better land along with the sheep and the cows go to the rougher land and can clean up surplus grass in places that we can’t cut. It seems to work for us but it’s just another option