I'm with Whitey04.
The only signifigant upgrades to the X version is lower center of gravity TVPs and easy access diffs and tranny.
BUT, the easy access comes with the price of structural weakness. The X tranny case cannot handle a more powerful motor than stock. HPI recommends that you install the old style tranny case if you want to use the K4.6 or other bigger motors. The ease of access became a non-issue with my old Savage. After I had wrenched on it a couple times I learned to dismantle and reassemble it easily. After I did the diff mod, I only had to service the diffs again once in three years.
You can also get a great deal on the older Savages used.