1) There is no good thief combo to really fight assassins. They're better in every way than a thief. Which is why you can cripple them so they can't fight, for example as a trapper or a poisoner. Absent that, the only thief that has third attack (and thus a chance in a "fair" fight) is a thug, but in a majority of straight-up fights assassins have better maledicts and damage options. If you have better eq or vuln-hitting, then maybe cheap shot can carry the day for you unless he flies. If he does, post backstab you can't really do much to him while he kans/kote/throw/kicks you around with your pathetic attempts to gouge and stuff. Nevermind the upper levels where trance is a factor. Some would say a full binder can kill anyone, in my experience garrotte and key bindings fail too frequently even perfected. (Practicing bindlegs/bindhands is very hard, they hardly improve at all.) But it is certainly possible to kill anyone (not mummy/lich) with a binder, however I think it's more of a theoretical possibility.

2) Knife is one round, gouge two. Knife can be taken by any thief, gouge is limited to thug. Knife can be used to initiate a fight, for gouge you need to be fighting. You can flee/knife very effectively against both mobs and people.