Quick update here. I snagged a SP belt/holster/V2 DSLR plate from eBay and separately a V1 lens collar plate. Used them this weekend.
WAY nicer than neck straps. That said, I did sometimes have the 300 on a strap around my neck along with the R7/70-200 on the belt with the lens plate. I would just move the R7 from lens to lens as I needed although I could have put the 7D2 on the 300... but it doesn't have tracking. . Overall, worked great. Yes, it was a lot of pressure on my hip when I wore the camera for a while but it wasn't too bad as long as I was moving (which I wasn't that much, but at football or soccer I would be). It was nice to be able to just let go and still not have weight around my neck and shoulders. When I donned the much lighter EF 55-250 it was REALLY nice.
1) Nice to be hands free. Secure.
2) Easy to remove/replace the camera.
3) Not as tactical looking as some other options (but still a bit).
1) the weight on one hip when I was standing still would give me some hip pain - more of a tingling - after a while. Tightening the belt helped.
2) squeezing through doorways, you just have to get used to the extra width.
3) the V1 lens plate has no hole for a monopod, which I am thinking would be a nice feature, although I suppose an Arca monopod head would be a good solution for this as the V1 plate is Arca compatible.
4) the mounting ball sticks out a bit, making things a bit tighter packing the gear away in the bag if you leave the plates on.
I will keep an eye out for an add-on holster for the other side.