Well, generally I'd say to go for the camera that feels the most comfortable in your hands, the one that has the better grip and the one that has the best overall feel. That would be the D7000, but I may just be saying that because I'm a Nikon fanboy
But if video capture is super important, You may want to stay with the 60D. I'd personally recommend that you go with the Nikon though, as I believe that having a camera that's comfortable to hold is more important.
If you stick with Nikon, you'll also be able to keep your lens collection from your D70, which is a huge benefit considering that tyou wouldn't have to buy any new lenses.
And regarding the buffer issue, I haven't had any problems with my D7000, shooting in large, fine JPEG. That's personal though, depending on what you shoot it could become a problem.