As good as Sad Wings of Destiny is, it is damaged by a couple of filler songs that were thrown in to replace the few classic songs that Gull Records allowed to be put on Rocka Rolla, namely "Epitaph" and "Island of Domination". Had "Run of the Mill" and "Winter" been on Sad Wings, it would've been a match for Stained Class. In fact, I just came up with just such a tracklist that would fit on an LP record, with songs spliced directly in from the first two Priest albums:
SIDE A (21:39)
1. Prelude (2:02)
2. Tyrant (4:27)
3. The Ripper (2:51)
4. Winter (6:33)
5. Genocide (5:46)
SIDE B (25:04)
6. Victim of Changes (7:54)
7. Run of the Mill (8:34)
8. Dreamer Deceiver (8:36)
The running time for "Dreamer Deceiver" includes "Deceiver", because I consider the latter to be the end of the former, not a separate song. This tracklist maintains much of Sad Wings' pacing and also gives a sort of progression to the album as a whole, with shorter, more metal-oriented songs on side A and proggy songs on side B. I suppose you could also toss "Cheater" onto Side A if you really wanted to.
Of course, you could go even further and tack on the unabridged "Caviar and Meths", "Rocka Rolla", and maybe "Never Satisfied" and/or "Dying to Meet You" as a double LP a la Twin Turbos, but at that rate you might as well pick up Hero, Hero (even if that compilation is a total cash grab made without Priest's consent), and new bands never, ever got double albums in 1974.
As far as the debate about Emperor, to me, Anthems is a prime example of how production quality is more than just fidelity. Anthems is a hell of a lot clearer than Nightside, but I find its production nearly unlistenable compared to Nightside's. Anthems was produced with absolutely no breathing room in between the instruments, instead seeming to fill the entire soundscape with homogenous sound--every instrument seems to come from everywhere, so to speak. There's no depth to the production, no sense of location among the instruments. Nightside sounds like a band; Anthems sounds like a randomly scattered jumble of instruments all playing at the same tempo and meter, but with no cohesion at all.