The first and third movements are excellent, as is the mezzo in the fourth movement (forgot who it was). I have only two complaints. First, I don't care for the unusually slow tempo for the second movement. Sinopoli tried to do something similar with the 2nd movement as well, and it just didn't work. And second, I'm a bit bothered by some the extreme tempo contrasts in the sixth movement. In particular, I'm not crazy about how Segerstam drastically increases the tempo at the symphony's very last cymbal crash - the climax of the long brass chorale. That said, however, the concluding section is excellent (where the two sets of timpani go back and forth on the tonic and dominant notes). As you stated, I would also take Kobayashi - and number of other ones - over Segerstam. But Segerstam's best moments are extremely good indeed. One could do far, far worse (Haitink/CSO sure comes to mind).
Barry