Head 2008 USA Mojo XP Heatfit Pro Ski Boot vs. Head 2008 Mojo HF HeatFit ski boots
It appears to me that the Mojo XP has a shell based on the Raptor boot, and that the regular Mojo has the S line shell (roomier and probably softer). The XP is the higher end boot as of now.
There is at least one HEAD dealer on the forum that might have both boots on hand and can give you more details.
i don't have either boot in stock but Richie is correct the XP is the 98mm raptor shell the mojo HF is a 103mm S line shell, other than that the difference between the mojo[s] and the S line/raptor is just graphics/liners/zeppas