I have just seen that in last year's Tryfan Downhill Dash, the first two finishers were women. There were only 8 competitors altogether, and the times were not specially fast; but the result is notable, since I get the impression that the gap between male and female performance tends to be greater in downhill lunacy than in standard fell races.
http://www.eryriharriers.org.uk/tryfan-downhill-dash-2/ but I haven't seen a full set of results.