As requested, here is a head to head comparison of these two lenses, with and without the TC14EII, TC17EII and TC20EII. This is not really a fair comparison, given the magnification advantage of the 500/4, but I am conducting the test to answer several requests for a comparison between the 300VR and TC17EII vs the 500/4: both at 500mm. I am not that great at lens testing, so bear with me. I started with the assumption that the reason your buy these lenses is to be able to shoot wide open. Second, most of my shooting is in the 30 - 100 ft range: the test shots were at about 35 ft. I am assuming that you are not getting closer to the subject, and are trying to decide whether to buy/tote the 500/4 or go with the 300VR and a couple of TC's. To be consistent, I shot in JPG fine, normal sharpening, auto WB, ISO 100, Matrix metering, Aperture priority with the lens wide open. I shot indoors because there is a storm passing through, I wanted consistent light and no wind, and I wanted to get this test done! I turned VR off on the 300VR. I corrected the WB using the eye dropper tool in Nikon Capture and batch corrected all the shots from the first one. Therefore all the test shots were taken under identical camera settings (except exposure) and had identical processing. The lenses were mounted on a D2X on a swiss arca B1 and gitzo 1348 with the lowest leg set retracted and 25 lbs hanging from the center support for stability. All the shots were taken with mirror lockup. The focus point was the square root key on the calculator. The major weakness to this test is the long shutter speeds required when shooting indoors, which could cause the results to be skewed by poor shooting technique. It would be better to find light where all the shutter speeds could be above 1/1000 sec. You will just have to trust in my technique. A second issue is that the exposures were not all identical. I trusted the matrix metering, which changed the exposure as the FOV changed. This makes the 500/4 and 500/4 + TC14EII shots appear a little sharper due to more contrast. Here is the entire view of the test shot at 300 mm In this series I have taken a 300x200 pixel crop from each test shot View attachment 17755 In this series I have cropped the same view and resized to 300x200 pixels. This is the same as trying to achieve the same crop with each lens and TC combination. This approach should favour the highest magnification, subject to the quality of the glass. View attachment 17756 Conclusions: 1. It is tough to beat the 500/4 and the 500/4 + TC14EII. 2. It is no competition between the 300VR + TC17EII compared to the 500/4. The 500/4 is clearly much sharper when shooting wide open. 3. The TC's degrade quality. The TC14 and TC17 show a very small amount of degradation and the TC20 shows a large jump in image degradation. I keep threatening to sell mine... The TC17EII works very well with the 500/4 and the 300VR. 4. The 300VR with VR on while tripod mounted does not work. I made a series with the VR on and had to reject them all.