According to UBM TechInsights' analysis, the A6's GPU is a triple-core PowerVR SGX 543MP3.
GLBenchmark results show it is around 2.4x as fast as the A5's GPU.
Here are some other GLBenchmark scores for reference, higher is better.
GLBenchmark 2.5 Egypt HD offscreen 1080p (C24Z16):
iPhone 5: 3003
iPad 3: 2820
Galaxy S III: 1708
iPad 2: 1545
Nexus 7: 1331
iPhone 4S: 1252
One X: 1197
Galaxy Nexus: 603
GLBenchmark 2.5 Egypt classic offscreen 1080p (C16Z16):
iPhone 5: 10349
iPad 3: 9877
Galaxy S III: 6662
iPad 2: 5489
iPhone 4S: 4535
Nexus 7: 4301
One X: 4041
Galaxy Nexus: 1632
This thing is a beast.
