>I even use my 70-200 2.8 VRII in Dx >mode occasionally to get a little extra reach on my D800E.
This is one of those innocent remarks that can confuse unless things are clarified...
The term "reach" can mean different things to different people. Some use it to mean tighter framing, in which case engaging DX Crop Mode can help if you're sure that the outer area of the scene contains nothing of interest - but staying in FX cropping afterwards gains flexibility at the expense of larger file sizes. On the other hand, many use reach to mean "more pixels on the subject" - and in that sense using DX Crop Mode does not make any difference.
Regarding the 17-55mm lens, I would aim to change it for a 24-70mm or equivalent to allow me to use the full FX sensor.
By the way, the D800 has about 16MP in DX Crop Mode, not 18MP