According to MWD:
When used to transform a noun into and adjective, the suffixes:
-al: of, relating to, or characterized by
directional; fictional
-ary: of, relating to, or connected with
budgetary
The distinction is only relevant when there is a desire to emphasize that the adjective describes something that is characterized by and not connected with the noun it modifies.
For example:
Evolutional Biology is a subfield of biology that studies the evolutionary processes that produce the diversity of life on Earth.
This seems to be an example where the distinction may properly be discerned. However, it is a restatement of the Wiki description which prefers the use of evolutionary in both places. Moreover, my browser does not recognize evolutional and redirects to search results for evolutionary biology. There is, happily, an entry for evolutional in thefreedictionary which provides links for other mentions in the wild.
Consider also - revolutional/revolutionary:
- The discovery of penicillin had a revolutional impact on our ability to treat bacterial infections.
- The American Revolutionary War was a military conflict that lasted from April 1775, to September 1783.
As used above, impact is more precisely described as characterized by revolution, than connected with revolution which is better used to describe the Revolutionary War in the second sentence. Again thefreedictionary has an entry for revolutional, albeit sparse, likewise MWD.
With their prominent placements in both definitions, of and relating to can serve to make the case that the two suffixes are synonymous and other factors better determine which form to use. Not even thefreedictionary has entries for budgetal, directionary, or fictionary. It’s probably something to do with their etymology, but that’s further beyond the scope of this question.