[dalke]

http://www.asu.edu/clas/sirgtools/ecology-1991.pdf says that Pogonomyrmex rugosus travels at 0.1914 * T - 1.983 meters per minute, for ground temperatures T (in C) between 20 and 40. This is roughly 3.8 m/minute or 60 mm/sec.

The equation for Messor pergandei is 0.0878 * T - 0.1724 or roughly 40 mm/sec.

So 50 mm/sec seems quite possible.

[lifeisstillgood]

I have just realised this conversation has become about the average speed of an unladen ant, European or Otherwise.

[dalke]

Both laden and unladen, in the paper I linked to. ;)