Wait a second... Unless the codex specifically says otherwise (Or the gauss flayer has been raised to STR 5, which is cause for celebration in and of itself), gauss flayer arrays are defensive weapons... Meaning a Ghost Ark can fire both arrays even when at cruising speed, and, If I understand how open-topped vehicles work, can fire both arrays and let the warriors fire (as it's non-defensive weapon) and move 6 inches. That's... A game changer in that discussion. (The other possibility is that moving 6 inches will allow only 1 warrior to fire. I've never had to deal with an open-topped tank before, so I don't know how firing out of one and moving works).