Photoshop runs sluggish while working at 66.7% Magnification....but runs fine in 50% and 100%.

Anybody else have this problem?  When I'm working on a multi-layered 300dpi, 16x20" file...at 66.7% magnification...and I resize one of the layers with the scaling command, it gets VERY laggy...to the point where I can't resize that layer with any kind of precision.  It's annoying.  
But when I change the magnification of the working space to either 50% or 100%, that lag is gone.  Sure, the quick answer would be to just use the 50%/100% for resizing the layer...but in some cases, the 66.7% magnification is better suited for what I'm viewing.   
Anybody know a fix on this?  I didn't used to have this problem with earlier versions of Photoshop, such as CS.   But since I finally upgraded to CC a few months ago, this has been rather annoying.  
I've got plenty of RAM...so I don't see that as the culprit.