Mac running Pro presenter->
Matrox dualhead2go me ->
Matrox dvi plus->
Black magic 1 me 4k->
Blackmagic Sdi to hdmi converter->
Panasonic dw640k projector
Is there going to be a lot of latency with this setup?
You did not specify the resolution you were running and that could have an impact. I think you will encounter almost all your latency in the projector. It's native resolution is 1280x800 so it will have to rescale no matter what you send it.
I am not familiar with that particular projector, but my guess is it will have 4 frames or so and the rest of the system will account for less that a frame except for special transitions that could add a frame. It should be acceptable for side mounted imag screens. Do not position imag screens where a person can view the camera image and the screen without moving their head. Never mount the screen directly behind the speaker.