I would recommend the stand, so that your center is just below the screen (as high as possible without causing a problem with the image). My VP150 is partially within the frame/border area of the screen, just below the image.
You want to use a stand for 2 reasons... 1) to get the center closer to the level of your ears, and 2) to have it off the floor to help reduce direct sound reflections from the floor.
You may want to consider moving your main Left and Right speakers a little further from the wall too, so that less of the sound you are hearing is reflected off of the walls.
Nice job on the room, and I'm sure it sounds great now, and even better once you get everything tweaked into place.
