When I do malfunction clearance using slingshot, I rotate the gun ~160 degrees counterclockwise so that gravity assists in clearing the gun. When doing a TRB I find the rotational movement of my wrist to bring the slide into position, meeting my hand near the 160 degree mark, to be VERY fast and quite precise -- more so than bringing my support hand up over the top and reversing my grasp with that hand. Likewise when returning the gun back to firing position and re-engaging my support hand grip.
The closer in towards my body, though, the further up on the gun my hand goes during malfunction clearance. At a certain point, definitely by the time I'm in a close retention position, I find it natural to switch to overhand racking because that's how the mechanics work -- it's impossible to effectively slingshot the slide in close retention, at least for me.
Regarding chamber visibility: I don't need to see into the ejection port throughout the cycle, but I do want to catch a glimpse of what's going on in there at key points in the process. This is how I run a carbine, and I feel uncomfortable if I don't apply the same principles running a pistol. While I can run an effective clearance drill on a pistol without being eyes-on to what's going on inside at any point, I don't think it's the best way to run the gun if I have any choice in the matter.