Sorry to shatter your illusions, but there's nothing optimised or efficient about intel graphics chips. They are at the lower end of the performance scale. Turning off OpenGL/ OpenCL is the way to go. Perhaps Apple may improve this one day by integrating better graphics drivers, but even then the facts stick - a toaster doesn't turn into a space rocket just by using different sandwich bread.
Since this is a forum for beginners who want to learn Photoshop, im moving your questions to a forum where you can get the assistance you need.
I appreciate your underlying point, but swirling a paintbrush around is hardly a voyage to the moon.
Intel Graphics set to Advanced Drawing mode manage this basic task fine on my old standard-res machine, and they zip along with equal immediacy if I run Photoshop in "low-resolution mode" on the Retina
The question is why do I see such a lag in retina mode?
The obvious answer is because we are at 4 times the resolution, but if I enable the full-blown native resolution of my retina display in the OS (with QuickRes tool), Photoshop now occupies 1/4 of the screen and is essentially rendering like a non-retina Macbook.....but the lag is still there.
I just wanted to know first and foremost whether this is what other 13" Retina users experience or if I had an issue with my machine or configuration. Thanks.