Replacing Nikkor 55-300mm. Nikkor 70-300mm or better option?

I purchased a D5100 with the 17-55 and the 55-300mm kit zoom lenses a few months ago.  I eventually replaced the 17-55 with the Nikkor 16-85 (which I love) and I am now considering changing the 55-300 with a Nikkor 70-300mm f/4.5-5.6G IF-ED.  I only have about $600 to spend so this fits in my price range,

My reasons for upgrading are that I want internal focusing so using a polarizing filter is easy.  I want the manual override on the AF.  I also want sharper glass (not sure if the 70-300 is any sharper than the 55-300?).  I want to have a good all around zoom range when combined with my 16-85mm zoom without a huge overlap.  The fact the 16-85 and the 70-300 use the same size filters is also and added bonus.  I currently use my camera for a little bit of everything, landscapes, portraits, wildlife etc.  I will be keeping both my kit lenses as I hope to purchase a D7000 body in the future and will give the D5100 with original kit lenses to my wife to learn on.

Before I purchase the Nikkor 70-300mm, I was wondering if anyone had any suggestions for a better alternative at no more than $600 that will meet all my criteria.  Thanks.