The only specific differences between an xONE3 and an xONE4 is the price and that you can 'touch' 4 continents rather than 3.

A secondary difference is a result of the continent sector limitation between the two. While you have the 20 segment limit in all xONEx's it's far easier to get 20 with a xONE4.

With a xONE3 you can have 6 N/A segments plus 4 in both the continent of origin and the remaining continent giving a total of 14. You need to be very creative to get six segments comprising your intercontinentals.