My understanding is that it doesn't matter which hose you use for any of the brakes as long as you have right barb in the end of the hose. I've just put a bh90 caliper on a bh59 hose and while I've not tested propperly, it's stopping me and not leaking.
@snottyotter what is the cheapest 2 pot BH-90 caliper can I buy?