I tested the Kingston 8GB class 10 micro SD card using ATTO Disk BenchMark v2.46
Write speed was approximately 7.5 MB/sec, Read speed was approximately 12 MB/sec.
I requested an RMA from Kingston and returned it for an exchange. The new one measured:
Write speed approximately 7 MB/sec, Read speed approximately 13 MB/sec.
Compare these to a Kingston 8GB micro SD class 4 from 2 years ago, which measured:
Write speed approximately 9 MB/sec, Read speed approximately 16 MB/sec.
Or an ADATA 8GB micro SD class 6 (FWIW 1st one of these had to be exchanged too):
Write speed approximately 7 MB/sec, Read speed approximately 16 MB/sec.
Conclusion, unless an application only needs to read quickly, where cameras for instance need to write quickly, I would not buy this SD card again for class 10 performance, since I can get the same result with cheaper claas cards, or better performance with another brand. I also tested each card in my Nikon DSLR, results tracked the Benchmark testing, measured as number of pictures in a 20 second period with the shutter button held down.
I recently bought a Wintec 16GB class 10, same measurement setup indicated 12 MB/sec write, 16 MB/sec read speed. Besides the wintec actually doing what it was advertised to, these results indicate nothing in my hardware was keeping the Kingston card from achieving 10 MB/sec if it had been good enough.