Hi Chief.
An angle grinder is the ultimate lock pick - there are not many (none ??) locks that will withstand a grinder and cut off wheel.
From what I've seen most bike locks are not very good quality or if they are, the locking mechanism are a bit sus.
I think your idea of a good,
thick chain with a quality pad lock, like innerpicked's suggestion of an HS lock with an Abloy Protect cylinder is probably the way to go. Then again a large enough pair of bolt cutters will cut a chain but someone carrying one would stand out. A friend of mine had his expensive bike stolen from outside his place of work. He had a pissy little chain and the thief used a small pair of bolt cutters that was then left where the bike was.
You could use a thick wire rope. These are hard to cut with bolt cutters but are a pain to carry around.
Now days with battery angle grinders not much is totally 100% safe.
The best thing would be to make it as difficult as possible to steal and obvious that someone is trying to steal it.
Things like where you park it etc.
If it is worth that much, you could get it insured if the rates are reasonable.
Maybe our European, especially Dutch, friends will have some better ideas.
Cheers.