Not sure Mav. The SBK3's are sintered and they have been known to chew the cast iron rotors. Bendix MF, which are again sintered, seem fine though. I guess you'll have to wait for someone with real life experience of the EBC pads
Wondered about this myself so have avoided using EBC HHs on my cast discs, I was using Ferodo Reds but as I can't get them anymore I have been using Ferodo CP911 Stars
The HH pads are designed for use with stainless steel or ductile iron rotors. You will experience accelerated wear and elevated heat levels which are the last thing you want with a cast iron rotor. More heat means more thermal expansion-induced stresses in the disc and their tendency to shatter under severe race conditions is the main reason why a number of race organizations ban the use of non-ductile iron discs. Cast iron rotors give significantly better braking than stainless because of their higher coefficient of friction, but I'd err on the side of caution here. I'll second the vote for Ferodo CP911* pads.
Shazaam's reply certainly makes me feel happier with my choice, I have always got my Ferodo pads from DTR, Denis Trollope Racing in the Bristol area but pick them up at the club racing venues he attends, Next weekend that will be Darley Moor where North Glos race club have a two day meeting.
Got EBC HH pads on my SPS cast iron floating disks. They have been on there with EBC pads for just over 7k miles now after replacing the supplied carbon lorraine pads (after 5K)as they were not a patch on the EBC. If you look closely there is some visible wear. I reckon probably another 10-15k and the disks will need replacing. The wear is in reallity no problem what so ever (25k+miles). I think your more likely to wear the carriers out before the disks in normal use. The only downside is they are useless in the wet.