Its an enigma, I'd put the Welsh performance due to the fact that they are playing for artificial teams with no history and no supporters. The Irish players are playing for provinces that have 100+ of history and a real connection with their fans. The 3 Irish provinces would easy be in the top 10 in Europe for average attendance over the course of a season.
Wales have won zero Heineken Cups and one Amlin Cup (2nd tier European comp), and have had one final appearance. Ireland have 6 Heineken Cups, one Amlin Cup and 3 losing Heineken Cup final appearances.
If you look at overall wins in the 6 nations Ireland were leading it in the first 10 years, their lack of championships was due to a mental block against France. A couple of years of regression under Kidney has reversed that now but hopefully we are getting back on track. Overall match wins in the 6 nations are similar for Ireland and Wales, however Wales have more championships due to the boom and bust nature of their team. Lets not forget Gatland was close to getting the chop in 2011 after 3 miserable years for Wales, he gambled on backing his untried youngsters and it the rest is history as they say.