Genghis Khan and William Wallace. Gustavus Adolphus would be nice too, but specifically Wallace and Genghis.
I want to see Hercules in other Classes, unAltered.
No, everyone just thinks of ways to beat him. As for everything else you've described, I'm not entirely sure how much of that is true. Gilgamesh never faced off directly with Ishtar, so... yeah, I don't know where you're getting most of that. I don't know what Gate of Babylon being the "Incarnation of Humanities Wisdom" has to do with being able to seal it, since it's not that. The treasures inside are Humanities Wisdom, not the gate itself. The gate itself is still a metaphysical existance that connects him to that wisdom, and in theory can still in certain ways be shut down. It'd just be an excruciatingly roundabout way to do it.
That being said, I won't say Odin -could- beat Gilgamesh, because we are still ignoring one very important thing: Nasuverse would no doubt make it so he'd be on even footing or lower than Gilgamesh. We already know they're making Strange Fake a free-for-all for "Who Could Beat Gilgamesh" with Alcides, Enkidu, probably King Richard, and a freaking Horseman of the Apocalypse, but as of yet none of them have directly beaten Gilgamesh. And I pray they day Odin appears in Fate/ never comes. So that those who have argued above will still maintain their wonder about this topic.
You're also forgetting that Odin would still be going by Fate/ logic, which as I pointed out above, thos facts have been stated in canon series. A powerful figure, yes. I'm not sure where or on what grounds you're getting he could basically take away Gate of Babylon however, but a well renowned figure of Norse Mythos whose abilities can't be gauged till he's in the series. After all, let's face it, we can spend hours upon hours, weeks upon weeks, years upon years looking up all the Norse Legends, Mythologies, and Texts that describe anything, everything, this that and the next thing of what Odin can do. But if Type-Moon says this is what they can do, and Odin isn't as powerful as all the things that have been said about him in lore are there, then that's just the way of it.
No real way of knowing. All we can really say for sure is he'd be weaker than Thor. (Thank you Magical Girl Illya anime) And Gungnir is a bit weaker than Gae Bolg.
While I don't disagree with the answer, since when was it ever stated in any materials or instances within Type-MOON produced works, that Clarent is a reforgery of Caliburn? The way it's described in Fate/, it's understood to be a different weapon entirely.
I believe that, regardless of rank, it depends on the manner in which he is attacked. If it's an attack of phyiscal nature, or magical that hits physically (Fireball, stone slab, or blade of energy), it is first reduced in power by the armor, and even if it punctures the armor, the armor still resists the damage, causing a rank down in damage. However, if it's not physically striking or damaging (Curses, command seals, or the like) then it won't really be affected by Armor of Fafnir. And of course there are those attacks that are either A. So Powerful they override his defenses, or B. Just shred through it like butter. Ea/Enuma Elish and Excalibur are good examples. But it's defenses are pretty much why Sieg survived Clarent Blood Arthur. Without it's resilience, he'd have died during that attack because, like Godhand, it wouldn't lessen the damage taken.
Due to the nature of the original Prototype being somewhat left in design stages, those are the only constraints known of Excalibur Proto. And to our knowledge, there haven't been any others made from Prototype: Fragments.