As for the extra height & bulk for U2, as long as the design can absorb it then fair enough - but also as long as this will be deemed one of those ubiquitous 'landmark' buildings and will not set the level for the area.
Why? I really dislike the aesthetics and even the idea of 'landmark' standalone towers which dominate entire areas of the city. Someone in the other thread posted a series of photos of European cities which have tall buildings. The ones which adopted a "clustered" approach to tall buildings - Frankfurt, Paris, etc. - are far more appealling than having individual towers dispersed around a generally low rise city. I'd rather have this, the Point "tower", Heuston Gate, the Barrow St./Thomas St./Tara St./etc. proposals all bunched together somewhere down the docks instead of ending up with having the low rise historic bits of the city compromised by "landmark" towers.