There are two mechanisms for Wurtz reaction. Now if we have to compare the relative rates of reaction then how could we do it?
In one mechanism there is a generation of a free radical while for the other there is the generation of a carbanion. The order of effects that determine the stabilities of free radicals and carbanions are opposite and so I feel that comparing rates wouldn't be possible if we aren't given on which mechanism we have to compare.
NOTE - The halide atom is assumed to be same for two compounds for which we have to compare rates.