Is Google Maps the best engine to gauge distance and especially approximate driving time for various countries in Europe (Ireland, Italy, Spain)?
If it isn't the best (might be other resources out there that are more accurate) it is probably the easiest and most accessible.
One of the best for years has been www.viamichelin.co.uk. According to many posters, add a bit of time to their estimates.
In planning my European vacations I've had good luck with Google maps as far as estimating driving time to our daily destinations. Just click "Get Directions" in the upper left, input starting and ending locations, and it will give the driving time. It takes into account driving speed of the different road types. (You probably already know how to use Google Maps...I'm just giving info for others who may read this later.)
But on the ground once we get there, we use our Garmin Nuvi 770 GPS and the thing just amazes me with it's estimated time of arrival estimates.
When I put in our destination, it takes a few seconds to plot our route, then will give an ETA. It seems that regardless of the winding country roads we go down, or the number of little towns we have to slow down for, the actual arrival time is almost always within a couple of minutes of the initial ETA!
Of course, if we stop along the way to eat, or drive faster or slower than usual, it will update the ETA to keep it accurate. It's just amazing.
One thing I learned to do: when we arrive at our day's destination, before I switch it off I'll have it plot our route to our next destination, then take note of the driving time it computes. This lets us know what time we'll need to load up the car and leave the next morning in order to get to the airport or next day's destination on time.