Well, with around 25mb left on my C drive ( after installing the new Maps ) it still seems to function ok, so with a whopping 54mb, you should be quids in.
One nice little touch was also to show the nearest petrol stations when in navigation mode. I tried it out the otehr day - once I got it working properly. Have to say though that I ddin't have any problems with voice volume - it was loud enough to hearm though I did have the car stereo turned down - but the window was open so lots of traffic noise coming.
I think it is a little limited though, I wanted to do a search and soem of the categories are a little limiting, so cannot search for a Point of Interest in perhaps the same way as a dedicated Sat Nav unit - but hey ! It's free.