I might be the wrong person to answer, but I think for a long run like that, balanced XLRs are supposed to be better. Hoping a friend better versed in this will chime in for you!
Otherwise, get the beefiest shielded RCA you can... My vote goes to
Monoprice High Quality Subwoofer/Coax cable: its RG6 rated, double shielded, 18awg solid copper conductor... if you need long runs of that.
If you build your own with speakon connectors, I can't really comment as I don't have the experience yet, I'm afraid.
Hope this helps!!!