Your own logic should be sufficient to figure it out. Considering the variables, guidelines aren't particularly as beneficial as common sense. I'd suggest maybe get a laser-light to equalize toe-in between the speakers. Get a cubic one, so the laser shines consistently perpendicular to the face of the speakers.
I like Newbees post, but unlike Newbee, if you have no idea about the degree of toe-in, I'd start (or experimentally finish) with speakers' forward-firing axis crossing in front of your head. Oh, and if you proceed while the spikes are on, pivot on the same spike for both speakers, every time, or they'll move around the room. Good luck, I hate toe-in.
I like Newbees post, but unlike Newbee, if you have no idea about the degree of toe-in, I'd start (or experimentally finish) with speakers' forward-firing axis crossing in front of your head. Oh, and if you proceed while the spikes are on, pivot on the same spike for both speakers, every time, or they'll move around the room. Good luck, I hate toe-in.