MacBook Pro with Retina display of 15 inch and 21.5in iMac is featured with Intel Iris Pro GPU. Mac mini and iMac comes with Intel HD Graphics 5000 card at the entry level whereas MacBook Air has new HD Graphics 6000 and MacBook Pro with Retina display is having Intel Iris Graphics 6100 card that is faster and newer. Graphics processing unit (GPU) also known as Graphics card usually manages the visual effects and make a great platform for smooth gaming.
Again, Mac Pro is having 3.7GHz Quad-Core Intel Xeon E5 which is comparable with iMac 3.5GHz.