The "has to be bigger than my biggest" rule applies to me. However, I did mount a 4x4 that sored around 140, even though I have a bigger 5x5. The 4x4 wich is a few inches smaller, actually looks like a bigger deer. I would mount a 150 4x4 any day over a 140 5x5. While the Same number of inches of bone, the 4x4 will look much bigger. It's not all about the score.
If I ever shoot a unique buck I will probably mount it too.
I have also thought about mounting a doe to put next to the boys on the wall.