I'm located in Belgium, which is pretty central in civilized Europe. And there are 3 WoW datacenters in Europe for English speaking realms, Germany, Sweden and Paris.

Paris is closest to me (300km) and I have 60-90ms to all realms located there.
Frankfurt (600km) is a bit further and I have 25-35ms to all realms in that datacenter.
Sweden is roughly 1500 km and I have a 12 ms ping over there.

I'm often playing on US realms and depending on the coast I have 70-80ms pings to east coast servers (using an SSH tunnel). Definitely for pve you hardly notice it. But I'd definitely recommend grabbing an SSH tunnel, they go for 3-5 dollar a month.