Hi,
Something to keep in mind with vFRC is that the block size is for the application IO size, not the underlying NTFS/EXT file system formatted to a certain version.
But yes, typically MSSQL workloads use 64k IO size.
Check out my blog on sizing your vFRC cache correctly:
http://nickmarshall.com.au/blog/2013/10/31/rightsizing-vflash-read-cache-vfrc
Cheers,
Nick