I have just finished migrating the server to the new machine, including the website and teamspeak. So far everything seems to be smooth. I allocated now 12GB RAM to the Minecraft process, 2x the amount of before. In case we run short I could probably add 1-2 more GB but I hope this will not be needed that quickly :D
From my perspective the server runs much faster already, specially startup time and in-game when warping to a new area, the landscape builds up significantly faster.