The "Wrecking Ball Weekender"

Bruce Springsteen will wrap-up his European tour this summer with back-to-back shows in Kilkenny, Ireland on July 27 and July 28.  They are calling it the "Wrecking Ball Weekender."

I will be in London on those dates.  Any thoughts on the best way to get from London to Kilkenny?  How long will it take?