I have the Colorado 400T with 2.04 bios. It comes with Topo 08 installed, but just last night I purchased the City Navigator North America DVD and installed all maps on my unit. The total file size was about 1.8 gigs. I am guessing my experience should be simmular to yours. I used a new 4 gig Scandisk SDHC card ($38 US Comp USA). This is the high speed card. I chose it because I have heard horror stories about load times with regular cards (8 plus hours). As is, the entire process took me about an hour an a half. I used the GPSr today and it worked fine.
Observations:
When I first tried connecting with Mapsource to the connected unit, it said I did not have room. This is because I need to choose the SD card of my connected unit from a drop down menu. When first loading, Mapsource defaults to the hard GPSr itself not the card. There simply wasn't enough room on the unit's hard memory for all that data. Make sure you select the right card/drive from the menu.
Before connecting the GPSr I tried loading directly on the card with my computers card reader. I got an I/O error as my reader does not recognize newer high speed cards. I had to clear the I/O error before I could anything else.
While the maps were loading to the connected GPSr's card I notice my computer about maxed out on resources and the core heated up quite a bit. My box is a P4 @ 3ghz with 2 gigs of fast physical memory and XP. I can see were computers with less horsepower may have a problem.