Upload & Sell: Off
From a "reach" and "image quality" standpoint you really need to be using the 300mm 2.8 VRII, the 400mm 2.8 VRII, or the 200-400 VRII......but then you obviously would one of the "hated tax cheat upper class 1% so denigrated on TV these days, and you would NOT be shooting with a D70s.
In your case the D70s would be more than adequately matched by the 70-300VR. It is a very nice lens that produces very sharp images. If I was in your position and wanted to step up past that I would go with the 70-200 VRII and the new 1.7 TCE III teleconverter............and would also be looking at buying a new D5100 or even a D700 (not a 7000, a 700).
In any case, though I have a 300 F4 and use it a LOT with a 1.4 TCE II to photograph hummers and other birds, it (as you noted) simply isn't going to track and focus fast with your D70. Essentially, you are "body crippled" due to the lesser capabilities of the D70 when compared to the newer bodies.