I don't have experience with EF crosses, but I do have some data on Bluefaced Leicester/Cheviot crosses. (mules)
I ran some percentages on 40 mules that we kept for at least 5 years. The ewe lambs were bred to lamb a 12 months of age.
I had 105% lamb drop on these 40 ewe lambs. Very few did not lamb at 12 months, and a few had twins. At age 2, they went to 160%, and their lifetime average was 176%.
This was in a grass based system, lambing on pasture in late April/early May. The ewes were flushed on fall grasses, and received no grain before or during lactation. You'd probably get a higher lambing % using grains or planted annuals, improved pastures, etc.
The ewe lambs were good mothers. They were usually more flighty and nervous about their lambs; cleaning them until you thought they'd lick the white off, constantly rushing about thinking they'd lost their lamb, running away when we'd go out to check and process the newborn, etc., but over all, settled in and raised their lambs successfully.
Lisa at Somerhill
www.somerhillfarm.com