Thanks for asking.
I think there's some confusion over here. Pro Theme has all the extensions that X Theme has to offer. Pro Theme also comes with Header and Footer builder using which you can easily design global or page specific headers and footers.
However, there is one key difference. Because of Pro Theme templating system, it does not comes with the Demo Content like feature that X Theme has to offer. So in Pro Theme, you can't import demo contents like Integrity 1 etc. However, as a replacement Pro Theme has something called as design cloud.
Regarding the upgrade, please consider following:
Who should use X Theme: Customers looking for rather easy to use product and want to have a website quickly can use X Theme.
Who should use Pro Theme: Though Pro Theme header and footer builders offer easy to use interfaces but it has some bit of learning curve involved. Once you are accustomed with the header and footer builders, possibilities are limitless. So, a user looking for more advanced featured and tools to design the website can use Pro Theme.
I am sharing relevant resources for Pro Theme that you can take a look.