The value will be around £4100 and all require a gold standard lock which also seems to be a bit of a minefield. Any advice appreciated
That must be a top spec! Look forward to seeing the photos.
The new highest Sold Secure lock standard is Diamond, it was introduced to differentiate too wide a range at the Gold standard. Mostly these are not new locks, just reclassified. SS have never published how well a lock does, just that it reaches the standard for that classification, so if resisting a grinder for two minutes is Gold, then those managing two or ten got the same badge.
Locking bike advice is a minefield, where, what and how. Then there's how attractive your four grand bike is, very attractive to someone who knows what it is, will take the time to find buyers and probably strip it to avoid recognition. Pretty much worthless to someone looking for a quick few quid, Halfords MTB's sell easier. I knew someone who's unusual folder, an Airnimal Rhino, was stolen twice and both times recovered within a few days. There's countless stories of peoples sheds/garages being broken into and the cheaper bikes taken in preference to the expensive ones. Of course there's also stories of specialist bikes being targeted...
Locks, I use two, D and chain, I have no illusions about them being unbeatable, I'm just hoping they make it more awkward. As locks get better, what it's locked too may become an easier target. My ideal - Both wheels locked to frame and to solid object or preferably two, both locks have to be removed to wheel the bike away. There's a new type of D lock that's more grinder resistant than anything before it, with not too much a weight penalty.
https://thebestbikelock.com/security/angle-grinder-proof-bike-lock/