If you look at the spectral sensitive curve of HIE at: http://www.kodak.com/global/en/profe...002_0333ac.gif
You'll see an peculiar curve (apart from a high UV sensitivity), it gets a dip around blue, rises through green to red, and drops of at say 880 nm. I could not find the curve of EFKE IR, but I seem to recall a more or less normal pan response, and a little tail into near IR upto 700 or so. So you need an heavy cut back on the visible part to be able to get an IR effect (this is more so for the new IR film of MACO, but at least you are than left with a "fast" speed of around 4 asa opposed to the 1-1.5 with efke...
Anyway, we are saying the same thing anyway I guess..