It will be the same, it also just uses LZMA. It has less headers, but that's not going to make much of a difference on 5M file

Compressed to 5mb. Original is about 20.

I haven't tried that one yet. I'll play around and see what I can find out. 7zip didn't perform as well.

  tar c -C ./build $(BINARY) | gzip -9 - > $(PKG_NAME_GZ)
  tar c -C ./build $(BINARY) | xz -z -9e - > $(PKG_NAME)

It should, if the compression algorithm is actually the same, just the format specification that differs.