Do the character rankings take everything into account? Destructive capability, speed, range, etc? If so...
Tohno Shiki: Possibly mid tier 8.
Ryougi Shiki: This is tough. Since her third personality gives her universal destructive capability and range, but her other stats don't match up. So, possibly mid or high tier 7? I'm not sure.
Emiya Shirou: He can create an Excalibur class weapon, but the usage would kill him. So he is probably on the same tier as T.Shiki, at least the Shiki vs Shirou interview leads me to believe they are on the same level.
Roa: Possibly the same tier as T. Shiki. He is faster, stronger, etc, but not enough for high tier 8. Not to mention Shiki has better eyes and instincts.
Arcueid: With Archetype Earth (whom is a different aspect of her personality) I would say she is a solid mid tier 6. During her path in MBAACC it's stated that she can melt the ice of the North and South poles, disrupt the axis of the earth and shift the continents. This was first suggested by Ciel and confirmed by AE, as she was going to destroy humanity by stopping the Earth's rotation. On top of that she has a really broken type of immortality/regeneration, arguably planetary durability during night time, back up from the planet, among other things. And of course multi continent/lifewiper destructive capability and planetary range (according to recent feats and statements).
Saber: I think she is fine on high tier 7. Her Excalibur seems to be city level, problem is that the number of times she can use it is limited.
Gilgamesh: He should probably be on low tier 6. Mainly because of his versatility. The all-knowing, all-powerful star (which is apparently semi-canon) allows him to pretty much download information from his opponents. Also his flying contraption which moves at the speed of thought and can fire magical nukes. And of course, Ea, a weapon that slices through space itself. This is assuming he is serious though.