You should be alright if you overclock. Dolphin is usually a dual-core application (though it can use a third core in certain situations with LLE audio), so it can't really take advantage of CPUs with more cores than that. A Phenom with two cores running 2.8GHz should be decent for a number of games, but you'll probably have to overclock it if you encounter any slowdowns. Also I believe your GPU should be able to handle 3x internal resolution (1080p).
As for Monster Hunter Tri, have a look at the Dolphin Wiki entry on that game. Also, feel free to look around on the wiki for other games. You'll find out if other users have encountered problems and possible fixes. You'll also find out what kind of hardware people are running games on and how they perform, giving you an idea of what to expect on your system.
As for Monster Hunter Tri, have a look at the Dolphin Wiki entry on that game. Also, feel free to look around on the wiki for other games. You'll find out if other users have encountered problems and possible fixes. You'll also find out what kind of hardware people are running games on and how they perform, giving you an idea of what to expect on your system.