I'd go with the RS-4. I think either get the Manfrotto mini ballhead with RC2 and the FastenR-T- (I used that setup before switching to Arca-Swiss plates), or just swap FastenR-3 for the Joby QR (keep a coin in the R-strap pocket for the little Joby plate).

I think you'll be fine switching out strap lug for tripod. Usually a tripod shot needs setup time anyway, a little more likely wouldn't hurt. The times when having both mounted matters most (to me) is when using a monopod with the 100-400, where I'm walking around then standing then walking again, lots of quick on-off.

For the 100-400, you'll want the R-strap attached to the tripod foot. Might mean a second FasterR-3 (I had 4 FastenR-T1s with RC2 plates, although now I just use a small AS-type clamp on the R-strap, and Wimberley camera/lens plates).

The RS-4 goes in the Toploader Pro just fine - both with the 100-400mm in the 75 AW or with the 24-105mm in a 65 AW (on gripped bodies). I just fold the strap and wrap it next to the lens barrel.

I often wear R-strap and a Toploader - the latter on my left side (strap on right shoulder), with the two straps crossed across my chest.