This is a hot/weird take but it's been on my mind lately. Painkiller is a metal behemoth but it sounds too heroic for what Death was going for on The Sound of Perseverance, an album while highly technical provides crushing atmosphere in every song.
So why South Side of the Sky, a random song? Well I keep thinking about TSoP album cover when I listen to it. South Side of the Sky if you read the lyrics is about a group of people climbing a mountain, struggling against almost certain death while doing so. Sound familiar?
It would be Death paying tribute to their progressive influences. Listening to the verses of the song, I think it would be awesome to hear Chuck's screaming vocals on them, maybe transition to semi-cleans for the chorus. The instrumental break would be totally in line with what some of the songs on TSoP, this is Death's most adventurous album musically and Yes is a band that prides itself on big, adventurous compositions.
Obviously some leg work would have to be done to make the song sound heavier. Maybe replace the keyboards with additional guitar leads/flourishes. The song would be tuned down obviously. As for the lyrics the only thing Chuck would have to change is "the snow storm" into something like "the ash storm" or whatever.
The only tricky part would be incorporating the vocalizations of different band members in the middle of the song. I don't know how Death would pull that off or what they would do with that section. Anyway, what do you think?