The percentage that's detectable totally depends on what the beer is. Ruthless Rye is 6.0% ABV and uses around 12% rye which is a good amount. If you were making a 7.5% ABV IPA you'd need around 20% to really notice it.
I made a black IPA with all Green Bullet hops and I'm not sure that I'd use them again as aroma hops. I had to wait an extra two weeks for the aroma to die down before I liked it.
It's a great hop. Stone Pale Ale uses Ahtanum for all it's late additions. If you can find some of that around it'll give you a great idea of what Ahtanum can do.
I had an onion beer recently and he used 6 sweet onions that he roasted in the oven for 5 hours and just scrapped it all into the boil. He also added some thyme at the end. It was like cold french onion soup in a glass. I'm thinking an onion barley wine could be fun.
Maybe Super Alpha or Southern Cross from NZ. Possibly Citra but the lemon flavors of Citra is a little different than that of Sorachi Ace and fades faster.
I really don't think anything will taste like Sorachi Ace. Is there a reason you can't just order Sorachi Ace and brew something else...
When I add banana to beer I just mash it up and let it sit on the counter overnight to convert and then just add it to the boil. You get a ton of banana aroma that way that you can't get with yeast.