This might be a dumb suggestion, as I'm not sure if I'm missing something here, but...
Why put ANY expensive cable in your ceiling if you're unsure if it's the right one? Why not run a 2" PVC pipe behind the sheetrock to an appropriate position, then put a single nail in the sheetrock at that position, so when you paint it you'll remember the spot. Afterwards, either the tiny hole from the nail itself or a small added mark will identify the location for you in a year or two or whenever you're ready for the projector. THEN you can go through the sheetrock and fish the appropriate cable through. Hell, you can install the pipe with a string already through it.
Basically, you're giving yourself an easy way to install the projector later without committing to it with $$$ or by cable choice...
