Greg, the equilateral triangle idea is a good one and it's what I always use, with the speakers slightly toed-in to point at the ears. Since except in your hypothetical example you can't make your room wider, if possible sit a few feet closer. Another point is not to have the woofer cones an identical distance from the nearest three room surfaces(i.e. floor and two nearest walls); if they're about a foot from the side wall, make the floor and back wall distances different from that, to the extent it's practical. This helps with smoothness in the upper bass area.
