I haven't skied the Supermojo 105, but one of those is a softer ski, and one is a super burly 2x4 that requires about 40mph of speed before it turns. I think that may be the Monster 104.
The 999 is a bit softer than the Mojo 94, and in my opinion, a bit higher performer. It doesn't have a small turn radius, but it bends up nicely and is an excellent crudbuster and soft bump ski. Very versatile, and stable, as you can ski it in a pretty long length without it beating you up, due to the softer flex. It is also laterally stiff. The Mojo isn't all that responsive and a little too damp for my taste. The 999, with soft early rise tip, just floats really well in softer snow, and has a bit more pop in the tail. It could be a great Western 1-ski quiver, especially if the skier skis in bumped-out terrain and bigger turns, and doesn't deal with ice too much. In the longer length, it is super smooth. Overall, this is one of my favorite wider all-mountain skis, as it works well for someone my weight and is super stable. The Mojo 94 is a nice ski, but it is realy damp and could use a little more oomph, IMO. Mostly, the 999 is a narrower (and slightly softer) version of the 1010: basically the same layup in a different width and sidecut. I have a pair of 999's set up for AT use, as they fit the bill well for a light traveling ski that works in any condition.