Jamie, I have often travelled on the Cork line and barely hit 90 mph, but the speed limit is 100 mph. I wouldn't get overly excited about the IR network statement nor would I rely on it as the definitive source of information.
If you don't believe me go for a trip from Athenry to Ennis, sit on the left hand side and observe the speed boards. A significant portion of the libe is placarded for 80 mph.
A lot of the Cork route is largely 90 not 100, Limerick J-Thurles and Charville and the Quad track near Dublin are Dublin side of Portlaoise. Everywhere else is more less 90 and not the 100 that many people believe.
One odd bit of speed signage on the route is once the Cork trains for Dublin leave Limerick J there is 100mph sign but when the direct Limerick track meets the line it 90. With signs are meters apart. So its either Cork can go 100 but ICR's from Limerick can't or someone forgot to take one of the signs down.
If the WRC is 80 then are these speeds being achieved as if they are then why is it taking so long?
Oh and BTW I think I will pass on traveling along the route again, twice was enough.