Thanks for the replies guys.
Good to know that it's been brought up before and that the PS team know about it. I thought it might be hard to implement, I wasn't joking when I said "if possible"
I know that sometimes even the most (seemingly) simple change or addition may need major recoding (which in turn could break other things, etc).
Cyphyr, thanks for the suggestions, I 'll keep them in mind. However, my current workaround is to make a separate "preview" render node, set detail to 0.1 (or even lower), AA to 1, GI detail & quality to 1, etc. Then I keep its render window open and just manually hit "Render" after every tweak. The result is very similar to that of the 3D preview, and at a
tiny fraction of the time ! The only drawback is that it doesn't auto-refresh, and that I have to remember not to keep tweaking while it's rendering. But it's so fast, that's easy to do
I hope the 3D preview does get improved in the future, but until then, the workaround works well enough. Oh, and of course it works with Crop Region, too
nick