I have a Garmin nüvi. Are there any all-in-one packages available? This side gives the possibility to compose individual packages, I often travel through Europe, so that the collecting of pois and it's maintenance is quite time consuming.
With the size of the file you are suggesting, and the amount of memory available in GPS units, it would be a non event.
Why not just get another GPS for using in the European countries that you are visiting ?