I have Legend and I use MapSource Metroguide version 5.
I have had Chattanooga, TN (home base) and Orlando Florida in at once along with the Cocoa Beach, FL area.
I have had some of the Chicago area and Chattanooga loaded at once. Then needed to add an another area of Chicago, so I removed Chattanooga.
I can keep Chattanooga, TN, Nashville, TN and Knoxville, TN all in at once - and it's almost capacity on the Legend.
I like the Legend (it's my first unit - had about 4 weeks) but if I had it to do over again,
I'd probably do the VISTA.
I have a notebook computer and loaded the mapping software there. So I can easily add/change maps while out-of-town.
As you select the maps that you want to download on the Metroguide software, on the left of the screen under the maps tab (? I think - working from memory here) it will give you the size of the areas you've selected for download at the bottom of that section of the screen. You can
see from that if your unit will hold the areas you're interested in at once.
Lots of luck -- really enjoyed mine and still
learning how to use features, etc.
BigAl.