Comparison of ASRock Radeon RX 7900 XT Phantom Gaming 20GB OC video card vs PowerColor Radeon RX 6900 XT video card by specifications and benchmarks. ASRock Radeon RX 7900 XT Phantom Gaming 20GB OC runs at 1.500 GHz base clock speed and has 20 GB of GDDR6 memory, while video card PowerColor Radeon RX 6900 XT runs at 1.825 GHz base clock speed and has 16 GB of GDDR6 memory. The TDP of the first video card is 300 W, and the second is 300 W. Compare the table of benchmark results to find out which graphic card is better.