Not yet, though we plan to do that - I have almost finished a blogpost about the SoftIndexFileStore (though, without performance info). When I've ran performance tests last time (before about 5-6 bugfixes during the review process), it seemed that SIFS is about 2x faster than LevelDB, but it all depends on
1) heap size and usage (how full it is, how often GCs occur...)
2) size of keys
3) read/write ratio
4) disk speed: SIFS would benefit from two disks (ideally at least one of them SSD) but I don't have machines with multiple disks ATM
How does it compare against the SingleFileCacheStore? And what is the general intuition behind when to choose SingleFileStore vs SoftIndexFileStore? You are probably going to cover this in your blog.
Performance-wise, SIFS must be slower than SingleFileCacheStore - for any read/write operation SFCS touches the disk just once, while anything else has to sometimes use more operations. The goal of SIFS is to workaround some common trouble with SFCS.
And yes, I am going to blog about that. In the meantime, you can checkout SIFS javadoc (and ask if it seems incomplete).