Neil, Your detailed description of your shooting style explains why you have different wants in a lens than I do. I just looked over a few bird albums of mine. In general my buddy shoots similar to me with his canon gear.
We use no tripod or monopod usually.
I find more flexibility with hand holding and cannot track flying birds well on a tripod. Granted I don’t have an expensive tripod with Gimbal head
Less than 5% of my images have a shutter speed <1/300 sec. More than 50% >1/1000 sec.
Iso gets sacrificed. I try to close down aperture 1 stop when I shoot with TCE. Most of my images are between iso 400-1600. Iso 400 only in fairly bright light.
He now shoots with a 5DMkIII and even goes up to iso 3200 with good results (good is defined as; could be on a magazine cover IMHO) Shutter speed is always kept in mind. Sharpest images seem to have fairly high shutter speeds. For flying birds I like to shoot at 1/1400 sec as a minimum.
For me I am probably okay in foregoing the expense of VR as it is mostly a non-issue with this type of photography.
Focus accuracy, Focus speed, lens sharpness, camera/ lens reach, and camera high iso performance are my main concerns.
Since VR adds substantially to the cost of this new lens I may be better off with a non vr 300 4.0 +/- TCE.
"Cameras and lenses are simply tools to place our unique vision on film. Concentrate on equipment and you'll take technically good photographs. Concentrate on seeing the light's magic colors and your images will stir the soul." Jack Dykinga