Only you can decide whether splitting the difference is worth it for you or not. There is no metric regarding what sort of bike category should use a longer or shorter stem. Other than meeting your own needs or preferences, its mostly a matter of reach as well as top tube length.
80mm could be a fine idea, although I'd probably leave it the way it is. You can look into a few other cyclcross bikes your size and see how they compare in terms of top tube length/reach and stem/drop bar reach sizes.