Did some IR training in a BE76 in Canada, and single engine in the missed with 2 onboard and near full fuel provided fairly good climb performance at sea level, even in above ISA conditions. Also did some IR training in the Seneca 1 and that thing was a pig. We only practiced engine failure in the overshoot simulated at altitude, and until you got the a/c cleaned up it was pretty much at zero climb even with the good engine firewalled. That assumed you got on the pedals quick and rolled five degrees into the live engine.
JAR OPS states perf B for MEP light twins. So, requirement to clear obstacles by 50 feet (I think) to 1500' after take off and a 1000'/5nm positive gradient en route clearance requirement as well as being able to hold altitude at or above MSA.
Used to fly Piper Chieftains for Air Taxi. That thing had a VG kit on it that upped our MTOW to 7348Ibs from 7000Ibs, however I would put money on the fact that if we'd lost an engine below 400' or safe obstacle clearance height, we might have just held altitude up to about 7000 on a good day. The SE service ceiling was supposed to be 13800...my point being that performance figures in the POH are based on a shiny new test aircraft!