I have a Refuge X and like it. I don't have a Soloplex, but I like the looks of it. They are fairly similar. From what I can tell, here are two differences:
1) The Soloplex is symmetrical front to back, while the Refuge X is not. In other words, the Refuge X has its apex a bit to one side (presumably where you put your head). I prefer this; it means that when I lie down, I have more space over my head. Some may not care, or feel that symmetry provides more storm protection (I think other factors probably play a bigger role).
2) The Soloplex's poles connect to the outside (they are placed on the ground). I would prefer this. The Refuge X might have a bit more space as a result, but I would rather have the ability to connect the poles on the outside. My poles get dirty, having poles on the inside means I have to enter the tent while setting it up, if I break a pole and have to use a stick I have less flexibility, etc. As with the symmetry issue, some may prefer attaching poles on the inside. That way, if you make an adjustment during the night, you don't have to exit the tent.
It would be nice to have them next to each other and compare the two.