Unless the opponents has his army split up and the gaul player has the element of suprise, ambush etc. there is little hope for the gaul player to do any thing. The most common competitive tactics was foresters and general body guard spaming. Hitting the guy with cazy amount of at 15attk arrows and taking out units that had strayed too far from the main. Chances is that the opponent will split his army up trying to chase down the foresters and thats when the gaul cav do the job, lots of micro management requires.

Problem with Gaul is not the cavalry, it is the infantry. They can't hold the line well and they panic too easily. Usually a chain panic will occurs and there goes the plan.