Wow! That's quite a difference;
The difference I have observed after visiting quite a few sheep dairies recently is down to
1) Genetics --some people just milk any old sheep whilst some spend considerable time and effort on recording and improving
2) Systems---this is perhaps where the largest difference is at the moment
I have seen 200l operations that milk sheep predominantly off grass and on the other hand there are operations that are mostly housed (little bit of grazing) , fed TMR, plenty of grain and will give 650l/head
Which route you go down would depend on market and opportunity I guess?