I have a system including D7000s and a D800, and may be replacing the two D7000s with either a D7100, D300 replacement (if one emerges this year) or a second FX body. Bear in mind that the way I use the D800 is multiformat, so I do use DX lenses on it from time to time and use the 1.2x mode in addition to FX quite a bit for action. The question is what way to go on a mid-range zoom. Basically, given the very promising tests of the new Sigma 18-35 1.8, indicating performance on at least Canon's higher-end APS bodies that competes directly with typical full-frame zooms on FX (no Nikon tests yet because no Nikon lenses in the sales channel yet), I'm trying to decide between a full-frame approach centered on a Tamron 24-70 VC 2.8 or Nikkor 24-70 2.8, a mixed approach centered on either the Tamron or Sigma, or a crop-sensor-centered approach on the Sigma. So the question goes (given there probably aren't any Nikon-compatible Sigma 1.8 zooms in the wild yet), what's everyone's experience with the big 24-70 zooms on both FX and DX, and does the color-depth, acuity, resolution etc., of the D7100 body compete well with high-res FX bodies when used with the best glass, or is it more comparable to lower-resolution, lower-dynamic range bodies? In an ideal world I'd have both but budgetarily I cannot do that.