The Shift and Enter seems to have it easier on the Cherry profile but the Spacebar and Backspace have a smaller margin as far as I observed, the DSA indeed clears well as it's thin and the stem is not recessed, similarly, I didn't notice any issues with SA either, as it's also not recessed and the bottom of the keycap is thin, I previously thought it was a shortcoming of the design, but it might as well be a design feature to support costar stabs, overall, SA keycaps are the best for costar stabs (as the inserts don't need to be clipped either) if you don't mind the extreme height of the profile (probably around 3x of cherry, since I keep my arms on the desk while typing, it wasn't for me) - With OEM's, I didn't experiment, however, with thin WASD's, I'm guessing the keycaps clear too (I remember a plastic sound that disturbed me on my first keyboard, a WASD V2 with reds, but I'm guessing it was the stabiliser insert issue that I linked before, didn't re-visit OEM's after these experiments)
I have a portable 8000* dremel and an 3000* set that came with this one:
http://www.amazon.com/Dremel-225-01-Flex-Shaft-Attachment/dp/B0000302Y8/ref=sr_1_4?s=hi&ie=UTF8&qid=1439213028&sr=1-4&keywords=dremel+3000 (the hobby 3000 kit as far as I remember) - If you're going to buy a dremel for this task, I suggest buying one that comes with this flex shaft, it eases engraving significantly, at the lowest speed, the grinding bit I linked earlier was pretty safe, It didn't heat/melt the keycap (ABS softens around 100C, so heat-wise it was pretty safe) - at the beginning I also slipped a couple of times, touched the top of a keycap once, but no damage was done, I also touched my hand a couple of times with the engraver, it seems ~safe too (it's a great grinding bit, it grinds heavily only when you push it, when you don't, it just sands slowly), but don't take my word for it :)
After doing this grinding a couple of times, it comes naturally now, at the beginning I was marking where to grind, but currently I just start with the stabiliser stem-holder area, grind the middle area well (the entire width of the bend should be cleared, not just the top of the bend), and grind the areas in-between so the wire clears without issues - it probably takes 3-4 minutes at most
(off topic) - as a comparison of profiles and stabs, SA+costar was the best combination I tried, GMK keycaps are thick too, comparatively the bottom of the SA keycaps are thin, but the sound characteristics of SA were more enjoyable, however, the SA profile is definitely not for everyone and it's very challenging on multiple levels (There are no R4 Shifts, the R4 and R1 are angles too extreme on opposite directions that limit the optimal usage significantly etc.), so GMK+costar was still the winner for me (those scoops tho ...)