Personally i'd go with the Nikon 300 + TC, but have you considered the 80-400mm? I had one a couple of years ago & actually really liked it. tbh I wish I still had it. I suppose it depends what you're going out to shoot & the light available, but it's a great focal range to carry round & good optically.
If you're mainly into distant wildlife or birds though, 400mm is a minimum imho so a good prime is the best option.....but at a cost.
btw,He who dies with the most toys, WINS!Nikon D800E & D700 bodies + Nikon 200-400mm F4 VR1, 50mm F1.4G, 16-35mm f/4G VR, 105 F2.8 VR macro, 70-300mm lenses. A couple of filters, Giotto tripod & ballhead. Lowepro Slingshot 302 AW