A lot will depend on how you want to use it really. I prefer to use a map with an old Etrex kept in my day sack in case the clag comes in and I end up lost and disorientated. I haven’t come across a gps with a large enough screen to be able to use it to navigate like a map.
I have had some fun putting points into my gps and going to them just to make sure I know how to use my gps in an emergency.
I wonder if the £800 might be better spent on a few map reading lessons and a cheaper gps unit so that you are more confident on the hill and probably rely less on the gps?
The above is only how I think and may well not fit your purpose?
Tom