A series is sort of what I did today
I remembered that the bokeh quality of the AF-S 50 improves by stopping down. So I went there again today, and fortunately that straw was still there.
I did not exactly find the same angle (did not have yesterdays image with me), but I think it's close enough.
Stopped down to f/2.8, the bokeh quality does improve a little indeed. However, the DOF increases significantly.
While I was on site, I tried the same shot with other gear I had with me. Below is the same straw shot with the D3x and the Tamron 28-75/2.8 at 75mm and f/2.8:
The DOF advantage of the larger sensor at the same aperture (not equivalent aperture) is pretty obvious.
I had another lens with me: the PC-E 85. The image below was shot with that lens, slightly tilted (around 1 degree) to tilt the DOF to follow the straw to the ground:
Even that lens struggles a bit with that kind of background.
-- Markus