Sorry - should have made it clear that I was replying to iand46 who had suggested setting the full screen speed display on the Nav V, and with that I assume a bit of wonderwheel twiddling would be needed every time you wanted to see the map and revert to speedo display. Your suggestion is how I have my satnav set, and I do sometimes find the red display when exceeding the speed limit useful, though I need to have a look to see if I can turn off the audible alerts as every time it beeps it cuts off the Sena intercomm link to my wife.
However, I find that display just a bit small to take in at a glance if I just want to quickly check my speed. I don't need glasses for distance but do need them for reading, so a bigger display is a big benefit to me and avoids me having to wear bifocals for driving - it's not that I can't read the display at all without glasses, but it takes that bit longer to get it in focus - obviously not everyone has the same requirement.
Fred