I too am trying to decide which I should get.
The 376C, the 378C, or the 478C.
It sounds like if I want pre-loaded (detailed) U.S. maps I can go with the 378 or 478 but th 378 maps make it "rcalulate" to some degree the trips you plan on the PC and then "upload" to it and the 478 does not.
The 376c comes with the GXM™ 30 smart antenna but you have to buy a Garmin card and the mapping software separately. On the 378 an 478 you have to buy the smart antenna but you get all the maps pre-loaded. What do you need the SD port for on these units?
If I get the 378 or 478 do I have to purchase separate software to do trip planning on my PC?
(I was going to get a ZUMO but Greg talked me out of it! LOL) I always thought that the display on the 376, 378, etc. chartplotter was the superior one for my old eyes.