GTA V, Meltdown/Spectre protection enabled:
Frames Per Second (Higher is better) Min, Max, Avg
Pass 0, 12.466310, 87.951523, 67.537834
Pass 1, 35.587948, 102.294464, 77.057365
Pass 2, 45.975742, 123.643021, 79.567863
Pass 3, 44.063927, 114.885742, 86.587761
Pass 4, 22.912081, 130.247345, 77.674034
GTA V, Meltdown/Spectre protection disabled:
Frames Per Second (Higher is better) Min, Max, Avg
Pass 0, 18.301443, 94.711319, 76.394928
Pass 1, 49.353958, 135.707306, 87.262985
Pass 2, 49.573666, 136.217514, 88.964317
Pass 3, 55.602509, 132.006226, 101.361748
Pass 4, 25.132448, 149.900314, 85.941391
Ghost Recon Wildlands, Meltdown/Spectre protection enabled:
FPS:Average: 50.48 Min: 34.72 Max: 56.16
GPU peak temp: 74
CPU usage: Average: 46.0% Min: 36.7% Max: 59.5%
GPU usage: Average: 76.1% Min: 65.8% Max: 86.1%
RAM usage: Average: 2.8 GB Min: 2.7 GB Max: 2.9 GB
Ghost Recon Wildlands, Meltdown/Spectre protection disabled:
FPS: Average: 54.50 Min: 45.14 Max: 58.59
GPU peak temp: 74
CPU usage: Average: 42.7% Min: 32.3% Max: 52.3%
GPU usage: Average: 81.9% Min: 62.5% Max: 92.3%
RAM usage: Average: 2.7 GB Min: 2.6 GB Max: 2.8 GB
It may be worth noting the higher CPU and lower GPU usage in Ghost Recon Wildlands with Meltdown/Spectre patches enabled, which may indicate TLB flushing is eating CPU cycles and bottlenecking the GPU in this scenario.
TL;DR
Meltdown/Spectre protection patches hit the performance of open-world games particularly hard on pre-Haswell CPUs.
Win10 Unpatched Win10 Meltdown Patch Win10 Meltdown + Microcode Patch
The Witcher 3, Ultra, No HairWorks 139.8fps 128.3fps 126.6fps
Rise of the Tomb Raider, Very High, DX12 121.6fps 117.2fps 121.6fps
Far Cry Primal, Ultra 128.4fps 127.0fps 126.2fps
Crysis 3, Very High 129.3fps 129.2fps 126.8fps
Ashes of the Singularity, CPU Test 35.3fps 35.5fps 35.6fps
Assassin's Creed Unity, Ultra High 131.1fps 131.2fps 130.3fps