A few more details which might be relevant...
- issue is visible in Develop with all Full Screen modes when set to Fit
- display res is 2560x1440
- only happens with raws from a Canon 10D
I'm thinking this happened with the noise reduction fix in the last release and is being provoked by some specific combo of screen res and raw size.
What Preview size do you have set? I believe using Fit Zoom will ask the display subsystem to resample the JPG preview that is the next largest from whatever the display size is, so your preview size will probably matter, although your display resolution is I think very similar to what a Smart Preview gets resampled down to so maybe LR is also doing something special with that particular size.
Is the pattern there because no NR is being applied to the preview? Does it change when you crank up the NR significantly or not? To me, the pattern looks like what happens when an image with micro-detail (no NR) is resampled to something almost a multiple of the starting image.
If it only happens with the GPU turned on then maybe the video card driver isn't behaving as it should.
Moiré patterns are easy to see in the Camera Raw plug-in to Photoshop, if you abuse the Detail slider and use Scrubby Zoom (click-drag the mouse diagonally) to set non-simple-multiple zoom values, similar to what Fit and Fill would do in LR, but with a wide variety of arbitrary zoom amounts, not just the two in LR.
Cranking up the Detail slider causes alternative light and dark pixel rows to be created which cannot be easily smoothed with NR.
I'd be curious if the OP's original problem with Canon 10D images might disappear if the Detail slider is set to zero, or lower than it is, now.
Here is what I see in the ACR plug-in for Photoshop if I set a zoom amount just slightly higher than 50% along with maxing out the Sharpen-Amount and Detail sliders:
Of course, with the detail slider that high (or anything very high), causes a maze pattern to become visible in the image, which causes moiré easily:
More to the OP's original point, even turning down the sharpening values to more reasonable levels, including a Detail=0, there is a slight bit of rectangular patterning in the sky at a non-simple zoom value:
....and here's the above file exported to DNG with my settings that exhibit the issue:
When switching from the Develop module to the Library module with 1:3 Zoom View setting it can take up to 15 sec. for the artifacting to appear. I have no idea what could be causing the delay, but again it appears to be due to the changes Adobe made in the display path preview rendering.
If anyone has LR 5 or 6 installed give it try. I'm guessing they won't exhibit the issue.