I think I would stick with GPSdrive for the GPS side of things unless there is something better. The maps that can be downloaded from mapquest have a lot more detail then what I have seen on Roadmap. This is just my first impression however, I haven't really done much with either software.
Of course GPSdrive still has a difficult system to import large areas of maps plus any large area will crunch on the diskspace. How can Streets and Trips get so much stuff into just a gig of space?