First I can't say whether or not a router would work.
Second, Mille, slower is better for the reasons natual stated however, the way around that is lots and lots of water. I have done 2 tanks now with a dremel with no problems. I would imagine if the bit fit a router it should work, just have an extra set of hands with a spray bottle on hand or use some putty to make a pool of water around your hole and keep it filled with water.