Be proud of your D300/s

The "D400" will have better (low and high) ISO capability than the D7000.

OK, I don't "know this as fact", but both the D600 and D800 have better performance in "DX crop mode" than the D7000, so it's a pretty reasonable assumption:
http://home.comcast.net/~nikond70/Charts/PDR.htm#D7000,D600 (DX),D800E(DX)

edit - you'll need to copy and paste that link, as DPR forum URLs doesn't work in this case.