What does a Garmin edge 800 have over a 500?

Afternoon all,

I am currently being severely tempted by the 800 on Amazon.

I currently have a 500, and will shortly be setting it up with HR and Cadence, oh and the HR is one of those cycleops ones.

I have a rubbish sense of direction, AND I like to ride places I have never been before - so I use the 500 heavily for the breadcrumb trail option - the minor frustration I encounter with this setting, is that I have to choose to scroll to a new screen to see my stats, you know, distance travelled, average speed etc etc
Would this not be an issue on the 800 - is there a facility to run the map on say half of the screen, and still have enough room for say 4 data fields?

Now I realise that with the open source maps the facility to navigate to places, around places becomes technically a lot easier - but I would still be looking to plot a route on bikehike/gpsies, and download it that way, rather than plug in a destination like a satnav - at the end of the day I will most of the time carry out circular loops anyway.
And I understand the benefit is that even though I still create the TCX file in the same manner, instead of a breadcrumb trail I get a sat nav esque image on a pukka map.

When using the 500, I run the breacdrumb trail at a 300ft (Or is it Metres?) zoom level and this is fine for 95% of the turns I have to make, but I guess the visibility of a map would make it unmissable, especially if it was combined with an alert of some kind.

So - aside from the fact you can have a proper map, is there anything else I can do with the 800 that I would not be able to do with the 500?

Something I want to achieve/create is some proper training plans - I have set a load up for running on my FR Edge 305, and these work a treat - to give you an example:
Warm up - press lap
1m @ 8.20 pace
1m @ 9.00 pace
1m @ 8.20 pace
Cool down - press lap

That is a basic one above, but just to give you a flavour of how I set them up - should I be able to do that both the 500 and the 800?

I've read mostly glowing reviews, but the one about water ingres does concern me a bit, especially living in this country - what are peoples experiences of this?

Be very interested to hear your views, am exceedingly tempted to buy one, just want to make sure it will provide me with enough of a positive difference.

Dan