Number of Segments versus Size
There is a way - not easy - to modify the old V3 TOPO or the old Road & Rec to have large segments... up to 8mb per segment (that's the biggest that Mapsource will handle).
The method for the V3 Topo is posted on the web.
I worked up configuration files to use the same method for Road & Rec.
The old Topo goes to less than 300 segments and around 1 GB.
The old R&R goes to 95 segments and 400 MB.
I also run the old Metroguide V8 (not locked)... it has around 1500 segments for the whole US and Canada.
I looked at converting TOPO2008, but ran into problems and never got back to it... it might be possible.
I don't know the segment size of other products....