These are two very different machines... almost an apple and an orange. The Pro 7 uses Windows 10 and accommodates all Windows programs natively. So far, there is not a model of the Pro 7 that includes LTE.
The Pro X is Microsoft's foray into a new "form factor" for mobile computing. It does not use the standard Intel / AMD chip architecture but instead uses a customized version of an ARM chip; ARM chips would typically be used in cell phones and some Android tablets. It offers longer battery life and LTE connectivity... but it is not compatible with certain Windows programs / apps because it runs them by emulation. Lots of games won't run, for example. That being said... if you want Office apps and browsing, this could be a perfect choice for you.