OK, first a word about how I listen to and rate performances. For me, I find that many performances fall in to a particular type of perforamance, ie: Driven, Romantic, Lean, Lush, Structural, Episodic, etc. Within each type of performance, I have a hierarchy of preference for the recordings I've heard. For example, Karajan's 60's beethoven cycle and Szell's 60's cycles are in a similar vien as Gardiners 90's cycle. Of the 3 I prefer Gardiner. Likewise, Walter's 70's cycle is in a certain style, as is Barenboim's most recent cycle. Of the 2 I perfer Walter. I would put Walter and Gardiner on similar levels of overall excellence, but in very different interpretive styles. And I wouldn't want to be without either of them.
Overall impressions of the Sawallisch set is that I like it quite a bit as a "driven" interpretation of the symphonies, but within that style I prefer Szell (especially in the latest remastering, which gives him even better sound), and above Szell I would place Gardiner. Both of these guys are very much driven sounding and focused on structure, but both find more time to stop and smell the roses during the incedental and slow music.
Of the slower and more romantic interpretations, there is Kubelik, Bernstein, and Barenboim. In this style, Barenboim is so far above the others it is almost funny. While Kubelik is just plain boring and Bernstein is willful to the point of losing the musical pulse, Barenboim somehow manages to keep the music flowing even at a slower pace. His rhythms are more sprung and his excursions in to the incedental music make you feel like you are on a guided journey, not like a person who has lost his way ala Bernstein.
Anyway, those are my thoughts. Sawallisch is certainly the most driven and "exciting" of the bunch, but I feel he loses some of the subtle and the beautiful in his performances that Gardiner, Szell, and Barenboim all do better in bringing out. Still, he's better than Karajan (who I didn't even bother including), Bernstein, and Kubilek, so he's certainly no slouch in this music. Just not to my taste as much as the others.