relative-rate of evolution
This kind of thing is normally calculated using the $K_{a}/K_{s}$ ratio, the ratio of synonymous to non-synonymous substitutions. It is not enough to count mutations for coding sequences, you should also take into account whether or not that mutation will actually change the resulting product.

There are various online tools that can help you do this, for example Phylemon:

http://phylemon.bioinfo.cipf.es/evolutionary.html