Stunning lens and the most versatile super tele of the bunch, IMO. Wonderful colour rendition, sharpness, contrast and superb bokeh. Used bare the IQ is nothing short of brilliant.
Add a 1.4x TCII and you have a brilliant 420mm f4 which you'd be hard pressed to tell the difference between it and the 300 bare. Add either the 1.7x TCII for a 510mm f5 or the 2x TCIII for a 600mm f5.6 and the IQ is still excellent, especially at the closer focus distances. With the TC's this makes for a very convenient super tele kit when you don't want to, or can't take longer focal lengths with you. I also have the 500 f4 VR and many a time I just do not bother with the 500 f4 and kust take the 300 + TC's.
The beauty of using TC's is that you get both the benefit of focal length of the added TC, but also with the benefit of the minimum focal lenght of the 300mm f2.8 VRII at 2.2mts. Essentially, a 420mm f4 with 1.4x TCII, 510mm f5 with 1.7x TCII and 600mm f5.6 with 2x TCIII all with a minimum focus distance of 2.2mts! Brilliant.
For birds in flight or sports action, the AF speed is super fast and most importantly, accurate. VR works brilliantly allowing easy 3 stops and sometimes 4 stops of extra handholdability on low light.
It's amazing how versatile this lens is and combined with the awesome IQ and relatively easy handholdability, it makes for a great tele lens. Highly recommended!