zerflin About a month ago PHP has stopped updating PHP 5, although no known problems have been found it is a good idea to migrate if possible. N1, N2, N3 and N4 are fully listed legacy and will remain PHP 5 for a few reasons including backwards compatibility for users running older software in production (yes this still happens), and the fact that the OS level is a far bit older then the newer nodes. The plan will be to sometime this year disable them from launching sites at all (we do give warning on dashboard if used and on the create screen and the API random create does not allow the older legacy servers to be used already). Then around 6 months after that we will be pushing sites off of the nodes. The time is not set yet but we are looking at September or earlier based on what kind of usage we still see.
Also the new nodes especially N9 and N12 are larger and have way more resources.