Most of the riffs in Leper are fast. You may not catch it because some of them sound primarily slow, but for instance, in that first riff, that tiny little palm muted part makes you move your hand and fingers pretty fast, though post people only hear the chords in that riff. And the riff before the one after the first solo are both obviously fast. Ghost of Perdition is much slower than Leper, except for that one lead after "devil cracked the earthly shell" but is probably harder rhythmically.