I also live in Germany and play on a US west coast server. My pings are between 200 and 500ms (it varies quite a bit from day to day). I haven't noticed a significant impact on play, but I've been here since I started playing the game, so your mileage may vary. Also, I'm not a PVP freak, and I can see how latency would have a far greater effect on PVP (especially Arena) than it does in most PVE encounters.

My advice would be to remain on your current server until you move to Europe, and see how much of an impact the increased latency has on your play style. If it's unbearable, then consider switching to an EU server. Bear in mind that you'll be dealing with folks for whom English is a second language (or they may not speak English at all). Not sure how much that will influence your decision, but my German is horrible, so I prefer to play on a US server. Also, that's how I keep in touch with a few of my friends in the States... chatting with my buddies in vent while running instances > long distance fees any day.