I haven't had a chance to check the latency for real yet but it's a ROE Black Onyx LED wall running through a Brompton Tessera M2 Processor (which states 3 frames of latency) from a DVI output. The projectors are Panasonic DZ13Ks running over SDI (can't find any values of latency for them however). The last option of adding the appropriate number of frames delay to the start of the video definitely sounds the best idea, and shouldn't take too long to sort out I guess (my first test of the set-up is the night before show day!)
On the point of multiple videos staying in sync. Would you recommend software or hardware decoding for this? I was semi-considering putting all 3 clips into a single 5760 x 1080 clip for guaranteed sync, but if you don't think this is necessary I'd happily run them separately. As this is my first use of MadMapper on Windows, I'd also be interested to know your recommended video codec for the platform?
Also, thanks for the Spout tip, that's very clever! Could well be useful for a last minute fine adjustment
Cheers for your help