I have decided to do some experiments for empirically finding the
optimal compression parameters.
The tool I have used was
This tool hunts for the optimal parameters by simply repeating the compression
with varying parameters looking for the optimal combination.
A run for one file may sometimes take more than an hour even on a fast computer.
The parameters that it tries are:
LC : number of Literal Context bits
LP : number of Literal Pos bits
PB : number of Pos Bits
YX : level of file analysis
FB : number of Fast Bytes
I have left the default parameters of dictionary size as 512 MB and
solid block size On. The tool uses the LZMA method.
The best combinations of parameters on several types of files were as follows:
I note that the best values were not constant even for files of the same type.
Conclusion: There are no best options, as each file may have its own unique
best combination. One may drive all parameters up to their limits,
but an improvement is not at all guaranteed.
The most common combination seems to be:
LC : 8
LP : 0
PB : 1
YX : 5
FB : 273
Some 7-Zip references: