I play catherine (fin, cre) on emporer and early rush all the time.
I use the rush not to eliminate my neighbor, but to grab important resources (luxuries), expand my empire, and secondarily weaken my neighbor.
The first trick is picking your enemy. Scouting is key. I try to attack one of my weaker neighbors (best if they don't have copper). I look for a target with 2-3 jucy cities (ones with good resources/locations) within easy stricking of each other. You want fresh cities (from a non-creative opp) so they have little defense bonus. While I'm building up my forces, I seek out barbs with the early units so they can get city raider 1 and II (I from barracks, II from barbs). I'll also preposition units near stategic resources at this point. I've found the key is to make sure you have a killer stack with 3:1 advantage for the first city before starting. At the first city, you'll lose some units, but if you plan your attacks right you'll leave with promoted units. I find after 3 cities, my killer stack runs out of steam, but by then the civ has been weakened enough to not be a threat and is willing to sue for peace.