Donwyn, I already had my eye on these - would you recommend them?
Q
Q,
That Decca set I've never seen before!

But how I'd dearly like to get my hands on it! Unfortunately I can't seem to locate it this side of the Atlantic (Stateside). Must be one of those releases that never made it abroad.
I admit I've never heard Söderström outside of her Janacek opera recordings (w/ Mackerras). So I can only comment on the high quality of her singing there. But based on that I'd jump on this Sibelius set if I ever came across it.
As far as that Isokoski disc goes, I recommend it without reservation, Q! Her rendition of Luonnotar is worth the asking price of this disc alone.
Another good one is the Mattila disc below. There's some duplication including Luonnotar. Though duplicating Luonnotar is no bad thing!
