Comparison of XFX Speedster MERC 319 Radeon RX 6900 XT Ultra Gaming video card vs Sapphire Radeon RX 6600 video card by specifications and benchmarks. XFX Speedster MERC 319 Radeon RX 6900 XT Ultra Gaming runs at 1.925 GHz+ 5 % base clock speed and has 16 GB of GDDR6 memory, while video card Sapphire Radeon RX 6600 runs at 1.626 GHz base clock speed and has 8 GB of GDDR6 memory. The TDP of the first video card is 300 W, and the second is 132 W. Compare the table of benchmark results to find out which graphic card is better.