Don't you trust iGo Europe maps? That's the easiest way to have EU nav in your device. Very hard to answer any question related to a car unit unless it is a very popular one. I used to have tomtom 7 and iGo 8.3 installed on the SD card on my WM 6.5 device, they both worked perfectly, except iGO took much longer time to re-calculate the route.
What make you think that iphone TT version will work; is it installed iOS 4.x.x? If you REALLY want to jump the ship to Tomtom, my best bet is to go with tomtom version for Win CE 5.