From a 1969 paper titled" The Meteorite Flux at the Surface of Mars". [1] The abstract says that Martian meteorites having a mass greater than 1 metric ton hit

From a 1969 paper titled" The Meteorite Flux at the Surface of Mars". [1] The abstract says that Martian meteorites having a mass greater than 1 metric ton hit the surface with essentially their space velocity, undecelerated. Those with mass less than 10 grams hit at terminal velocity, whatever that is for Mars. In between, I suppose there's a continuum of impact velocities depending on the mass. [1] http://adsabs.harvard.edu/full/1969PASP...81..399D http://adsabs.harvard.edu/full/1969PASP...81..399D (paywalled, but they show you the first page with the abstract, which tells the tale)