If you have a legitimate need for the line speeds you can ask Irish Rail and they will quite happily give you a copy of the latest numbers.
Despite the scare stories, Irish Rail's passengers numbers are actually holding firm at a time where Dublin Bus and Bus Eireann are in serious trouble. Numbers in 2010 were close to 2 million above the target agreed with the NTA, Irish Rail is still ahead of 2005 numbers while Dublin Bus is back to 2001 ish era
Rosslare, Westport and to a lesser degree Sligo are doing quite well. Western Rail Corridor on the other hand is a mess