Foolish heart:
You could check it out in detail here:
http://www.garmin.com/products/etrexVenturecx/. Looks to me as though the two key differences are that the Vista includes an altimeter and has a USB port so that you can download maps, waypoints, tracks, etc. from your computer. I make those assumptions from reading the bullet points at the above site. I am still exploring my Vista. You can set it to optimize routes for specific vehicle types: Bus, Car, BIKE, and to avoid toll roads, etc.
I received the bike mount this week, and have mounted the unit on my bike. Went out yesterday to test it out. Worked like a charm - and, because you don't need to illuminate the screen during the daytime, I am certain there is an insignificant drain on the batteries.
I took a 10-mile ride after dark last night just to see how convenient it would be after sunset. Again, it works fine, and you can set the degree of brightness for the display to very low or through several increasing steps to very bright. You can set the illumination to go off after a certain time interval, or to be constantly on. I like the dim, constantly on setting so that after I turn it on, I never have to touch the unit while riding to see my progress, estimating speed, heading, etc.
It's a very nice unit.
Caruso