Did a compression test of the content of some of the .gz data files stored by CPDN.
LZMA2 seems to halve the space used and transferred. I wish LZMA2 compression.

The uploaded file is already compressed in zip format / Deflate compression algorithm, the compression rate(compressed file size/original data size) is about 66.09%.
During my own compress test, compressing using LZMA2 with "best quality" and "solid" configured achieved a better (but not MUCH better) compression rate (53.74%), and the CPU time used in the compression process is much more(11 seconds for DEFLATE, and 41.9 seconds for LZMA2, tested on i7-6500U).