I'd go with the Zumo 660 which is what both the wife and I have. I used to have a Zumo 550 and only upgraded to the 660 so I could get the bigger screen and also stream music to my Scala G4 in stereo as the 550 only supports the HFP Bluetooth profile and therefore streams music in mono.
However, don't go for new. Look out for the Zumo 660 NOH. You can pick them up for about £320. They are factory refurbished to as new condition by Garmin but come in a white box instead of the fancy retail packaging. You get everything you get with a retail product, including the free map upgrades if new maps are released within 90 days of first use and the 12 month warranty. That's how I bought both units that we have and there is absolutely no difference between them and a retail product, bar the box and over £100.
To be honest, given that you can get these for £330 it always confuses me why people buy second hand units for in excess of £300. I presume they are thinking it's not a bad deal based on the retail price, not on the price that they could actually get a 12 month warrantied "as new" item for if they looked around.
You can pay £49.19 to Handtec and get a Garmin "for life" update package for the whole of Europe. You'll get all new map updates for 1 unit until Garmin stop producing them.
We've done plenty of Europe with ours, plus a lot of the UK and they've never let us down. A couple of colleagues also use them. One of them recently bought a TomTom Rider but took it back as it was, in his words, "fecking useless". He changed to the Zumo 660 and is like a dog with 2 todgers. I used to do around 60,000 miles a year split between bike and car due to my job and always relied on the Zumo.
Dae.