If vertical space wasn't limited I would have the same speaker as my fronts (M60's). I did find much better intelligbility when I turned my VP150 upside down, since the drivers were more on an angle to my ears where I sit.

My friend has Pardigm Monitors and he tried a phantom center, but I can tell there is a slight hole under the TV, it doesn't image it well enough since he has his fronts somewhat farther apart. Bottom line, some situations a center can help if its matched properly.

M60, VP150, QS8, HSU VTF2-MK 3, Marantz SR8002, Oppo BDP-83SE, 50" Panasonic Plasma