VirtualTexture performance is much worse on SM6 than SM5

1. Download this [Link Removed]. 
2. Launch it with "-game -windowed -sm5" 
3. Goto a position with "BugItGo 0.000000 0.000000 -12151.570176 -0.700000 -2.100000 -0.000000"
4. See the performance with "stat unit" and "stat GPU"
5. Launch it with "-game -windowed -sm6"
6. Goto the same position
7. See the performance with "stat unit" and "stat GPU"

The performance is much worse on SM6 than SM5, and it's easier to observe on low-end GPU, like NV GFX 980 or AMD Radeon RX 5700, but not much noticeable on NV GFX 2080ti or above GPU.