Never seen that idea on a commercial machine before, it must be a complete original. What do you do that requires a 2 in 1 solution?we needed a foam CNC mill and a foam hot wire cutter.
"Feed rates/wire speed" are related to the wire temp and foam density. On new blocks we often do a quick test to see if we need to change any setting. We have found differences in suppliers with the same density of foam and sometimes in different foam orders. The standard density (1lb I think) will run 800 - 1000mm whereas the high density could be 700 - 850mm. Extruded foam (DOW blue) runs 450 - 550mm. If the wire temp is turned up you can run a lot quicker but you can loose a lot of accuracy on a complex shape, it won't make to much difference for a packaging piece but for a custom mould it could be crucial, we tend to err on the side of accuracy not speed.
On the inconel we haven't found a pattern, sometimes a wire can last months (10 or 11) other times we have broke wires in quick succession, for no obvious reason. Other times it has been operator error: moving the independent axis to far or adjusting wire temp far too high. We try to have a number of spares made up ready to go, but it not a thing that we worry about too much. It's a pain in the **** when one breaks doing a complex cut in a large block, but **** happens, a bit like having your laptop stolen.