Hi there island neighbour (almost)
While I don't have a Garmin 750, attached are screen grabs from the latest Blue Chart g2 chart data I have on my Garmin plotter (using the Home Port PC software), which AFAIK is the same data set as you'd get and so you'll not get more underlying chart detail than this.
I've attached a few grabs at the most detailed resolution so hope that helps.
As you'll see, in complex areas of rocks etc (eg around the islands on file 3) the data you'd find on an Admiralty chart is approximated, which to me is a drawback, as often I'm wanting to find routes onto small islands etc, which can still be done. I just additionally carry an up to date online paper chart from Visit My Harbour plus Google aerial photo data.
Feel free to get back to me with any other queries, as I wanted clarity on this issue when I was about to buy.
From what I found, while this Garmin data is not quite the detail of a paper chart, it seems not that much better or worse than other GPS options. Though others on there will have different views - would be useful to see the detail on other makes.
See: Advice - best electronic chart options for chart plotter - North of Scotland / Orkney
Hope this helps
PS my horse came from Whiteness so know your area a bit.