Insurance is great - when you done with the shoot, returning home and will have time to replace the equipment. However I always get nervous at the start of the trip - if I loose my equipment, insurance will not buy me a new trip
True. But as I said, I have confidence in the setup. To be honest, I do usually hold the 600 II by the tripod foot when it's on the strap. But I let the strap take the weight.
As far as BR strap, I trust an anchor point I screw into the plate or body. I am not comfortable with a small clamp (e.g., the Kirk system) which could get loose and have camera crash to the floor.
You might think so - my experience has been the opposite. With the BR FastenR lug connected to a tripod socket, and the strap connected to the lug, the rig is swinging from that lug. That puts torsional stress on the screw. I used to use that setup - even with a tight connection and moistening the rubber compression washer prior to tightening (as BR recommends), it would come unscrewed on a walk/hike. That happened more than once (didn't fall off, but would have had I not noticed). I got in the habit of checking tightness a couple of times an hour, and at least once every couple weeks I needed to re-tighten the lug. The same thing would happen with the FastenR-T1 that I used with the Manfrotto RC2 plates.
Since switching to the AS system and the Kirk clamp connection, it's not come even slightly loose once. I've given up checking the connection at all. The lug is attached to the clamp with Loctite - that's where the torsional stress is, and with Loctite it won't come loose. The clamp has a good intrinsic resistance - brushing the knob won't loosen it. Plus, the clamp is placed so the knob is under the lens when attached to the body, and away from the body when attached to the lens - there's minimal chance of even brushing it.
Bottom line, after two years of using the directly connected lug, I learned that it needed to be checked often because of a tendency to come loose, and after a year of using the Kirk clamp, I have complete trust that it won't come loose unless I intentionally take it off.
An alternative is to ditch the sling bag and go with a Think Tank technical belt and pouches for individual lenses. I like this arrangement for ease of changing lenses.
I do something similar on occasion. I have a Spider Holster, another great carry option. I avoided them until they came out with an Arca Swiss clamp option. I don't use their belt, I attached the holster to a Lowepro Deluxe Technical Belt, and I can attach lens cases, a monopod holster, water bottle/phone case, etc., to the belt as well.