Comparison of ASRock Radeon RX 7900 XT Phantom Gaming 20GB OC video card vs XFX Speedster MERC 319 Radeon RX 6900 XT Ultra Gaming video card by specs 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 XFX Speedster MERC 319 Radeon RX 6900 XT Ultra Gaming runs at 1.500 GHz base clock speed and has 16 GB of GDDR6 memory. The weight is different, 1450 g vs --. The TDP of the first video card is 300 W, and the second is 300 W . Compare the benchmark results to find out which video card is better.