So I used my Epix's as a bike computer today... mounted in place of my Edge... I had the screen scrolling set to medium... I am happy to say the screen didn't dim during the ride.
There are 2 couple of fields/functions that the Edge 830 has which are not on the Epix.
1. Lights - the Epix can control them but the fields - number connected, battery level and beam angle aren't available
2. Food and Drink reminders - not possible - I was starting to use this so won't miss this...
But overall I might stop using the Edge altogether.