Lion wins with Tiger of same size
Male lion - photo by MazetMan (Flickr)
I agree the Tiger is (Siberian) probably one of the top 3 predators on the planet. A big male Siberian will way over 600 pounds and I think because of his thick coat could Kill a large African Lion. However if a Large (in his Prime African lion came across a similar sized (in his prime) Bengal Tiger my vote goes to the Lion. Here are my reasons...
1: (most important) The African male lion's main duty is to protect his pride from other male lions. He fights all the time! He kills other lions if he can, He'll help bring down buffalo and on rare occasions elephants.
His large mane is great protection against claws and teeth. He is used to fighting. He has fought for his food in the pride and other big cats as well. The Tiger hasn't. Although the Tiger has some awesome weapons his "heart" isn't that of a lion.
2: The African lion looks for fights...he is roaring all the time to warn other lions to stay away. He is always in a fighting mode the Tiger isn't.
In conclusion I do think a Siberian could just about take on anything with the exception of a large Brown Male (Kodiak 1000 Pound Plus) Bear or Polar Bear.
However a well organized pack of wolves, wild dogs if they have a mind to can just about match any predator out there.