My brass Sunset K4s is one of the best detailed steam locomotives I have. Coming out of the HO and N world, I don't see anything in O to be particularly delicate.
Now comes the next level question, once you experience a better brass model than the one you have does it ruin you further? The PSC K4s is even more detailed than my Sunset one and one day I'll track one down finances permitting. Likewise my Sunset brass P70 coaches are really nice, then I got some PSC ones. Oops....
My J1 isn't too shabby either.