As the days go by and developers get faster machines with SSDs, they keep breaking and slowing down machines that don't have SSDs, etc. (such as saving cache which obviously should not be a synchronous operation, but they have an SSD so they don't notice). I am sure this makes a difference, as I have seen it and fixed it. Do all of them have their home dirs and temp dirs on SSDs? (and obviously other hardware is relevant, just an SSD is an easy thing to forget). And if it's not an SSD difference, it might be filesystem. Maybe CentOS uses xfs which can be faster in some cases. Maybe your Ubuntu uses btrfs, which can be faster or slower wildly.
Also video drivers are relevant. Do they have the same driver? Maybe some use nouveau, the slowest driver available, and others use nvidia (proprietary), radeon or fglrx (proprietary)? Also different kernel versions have different drivers and may have some effect (I have seen many nouveau stability issues but not sure what to say about performance).
Also Ubuntu with unity uses compiz or some thing that changes graphics effects around severely affecting performance. I think you can't turn it off (unless you switch from unity) but you can disable some of the effects (the setting is not in regular menus... takes some digging).