fast compression & decompresser

pigz is a parallel version of gzip. 
Although it only uses a single thread for decompression, 
it starts 3 additional threads for reading, writing, and check calculation. 
Your results may vary but we have seen significant improvement in decompression of some of our data sets. 
Once you install pigz by (sudo apt-get install pigz) the tar file can be extracted with:

    pigz -dc target.tar.gz | tar xf - -v(verbose logging) 
    

#for decompressing 

use tar with the multi-threaded compression. Like:

tar -I pigz -cf file.tar.gz *

Where the -I option is:

-I, --use-compress-program PROG
  filter through PROG

Of course, if your NAS doesn't have multiple cores / powerful CPU, you are limited anyway by the CPU power.

The speed of the hard-disk/array on which the VM and the compression is running can be a bottleneck also.