rjsquirrel,
It is difficult to understand where you are going with this; if I were supporting the S92 against the EH101, One Engine Inopertative (OEI) performance would not have been the issue of my choice (for the reason I indicated earlier). However, if you wish to continue with it, it might be fairer to compare graphs for both aircraft.
The HV Diagram is not a graph that is used when examining winching performance - it is too general and therefore of little use. What would normally be used (if engine failure is being considered - which it might not under military conditions) is the OEI HOGE performance graph; the entry point would be (initial) on-task mass.
Even then it is more complex than the HV diagram, as density and wind would have to be taken into consideration. Such graphs usually have temperature and pressure (density altitude) as the constants with drop-down v hover-mass as the trade off. With some missions, there is the opportunity of taking advantage of some of the drop down - so increasing the on-task mass; this would not result in a ditching.
If one were to do these calculations for the EH101 and the S92, it is likely that the EH101 would be nearer to MTOM than the S92.