Every time the user goes through control panel to calculate the Windows Experience Rating, the system creates a new file in %Windows%PerformanceWinSATDataStore
You need to find the most recent file (they are named with the most significant date first, so finding the latest file is trivial).
These files are xml files and are easy to parse with XmlReader or other xml parser.
The section you are interested in is WinSATWinSPR
and contains all the scores in a single section. E.g.
<WinSAT>
<WinSPR>
<SystemScore>3.7</SystemScore>
<MemoryScore>5.9</MemoryScore>
<CpuScore>5.2</CpuScore>
<CPUSubAggScore>5.1</CPUSubAggScore>
<VideoEncodeScore>5.3</VideoEncodeScore>
<GraphicsScore>3.9</GraphicsScore>
<GamingScore>3.7</GamingScore>
<DiskScore>5.2</DiskScore>
</WinSPR>
...
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