Well, which is your favorite Sorabji etude, favorite Sorabji piece and favorite piano piece overall? And why?
It's never occurred to me to have a favourite Sorabji etude, or a favourite Sorabji work, and I'm going to sit on the fence as regards favourite/greatest piano pieces.
That said, the particular etude you mention is not one that I find exceptional: you mention "its gradual buildup(s), its sensuous harmonies, as well as the multiple emotional and contrapuntal layers found within" but all of these merits are plentifully in evidence in other works by Sorabji. I suppose that there are few works of his that rise from such comparative calm to such a climax in so short a span.
You've made me listen to it with a new attention, which is always good, but if I were singling out one of the studies (that are currently available) I might mention No. 26 or No. 36. Then again, perhaps I shouldn't, because there is a lot of exceptional music in the studies.
As for my favourite work by Sorabji overall ... I really struggle to choose one work from such a consistent composer. In fact, to choose one is immediately to regret not choosing another, which is why I was intrigued by your choice in the first place.