AMD Radeon HD 7990 's Advantages
Boost Clock has increased by 28% (1000MHz vs 780MHz)
More VRAM (3GB vs 1024GB)
Larger VRAM bandwidth (288.0GB/s vs 36.80GB/s)
1664 additional rendering cores
AMD Radeon R5 340 OEM 's Advantages
Released 2 years and 1 months late
Lower TDP (65W vs 375W)