Pull a four and use two and you can't go wrong. After all nobody looks at a wire coming out of the ceiling and says "damn, it has to many conductors"
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This.
I pulled 18/4 for my 2 wire detectors. Worked out very well when I found out that you cant have 2 wire heat and smoke on the same zone. I used 2 conductors of the 18/4 for the fire loop, and the other 2 for the heat loop. Everything is still open so I could technically run another wire if I had to (code reasons maybe?) but it was nice to be able to quickly fix the "goof up" and at least have the smoke and heats running again.