As mentioned by Blakesdean the Luton 321 operation is medium haul and not transatlantic so there could be a performance issue for longer haul 321's off Cork's runway declared distances and obstacles. Luton's runway whilst similar in length to Cork's has the benefit of no obstacles beyond the end of TORA in each direction ie TORA 2163m TODA 3243m. Whereas Cork is TORA 2133m and TODA 2194m.