AMD Radeon HD 7990 's Advantages
More VRAM (3GB vs 2GB)
Larger VRAM bandwidth (288.0GB/s vs 112.0GB/s)
1536 additional rendering cores
AMD Radeon 550X 's Advantages
Released 5 years and 11 months late
Boost Clock has increased by 22% (1218MHz vs 1000MHz)
Lower TDP (50W vs 375W)