LZMA is a lot slower than LZMA2 but can give better compression.
I don't know how much RAM you have on your comp, but increasing the dictionary size will reduce the size of the 7z, but it requires a lot of RAM for the compression process.
Increasing the Word Size has a minimal effect, but an effect nonetheless.
config examples for compressing C2C after deleting sources, debug dll and .pdb files.
LZMA2 unless otherwise stated.
dictionary-word ▬ 7z file size
64 MB - 64 bit ▬ 687 MB
64 MB -128 bit ▬ 686 MB
128 MB- 64 bit ▬ 677 MB
128 MB-128 bit ▬ 676 MB
128 MB-256 bit ▬ 676 MB
192 MB-64 bit ▬ 676 MB
256 MB-128 bit ▬ 675 MB
LZMA- 64 MB- 64 bit ▬ 679 MB
LZMA-128MB-128 bit ▬ 664 MB
LZMA-256MB-256 bit ▬ 658 MB
LZMA-1024MB-273 bit ▬ 653 MB (1 GB RAM needed to decompress...10 GB to compress)
The higher these numbers are, the more RAM and time it takes to compress/decompress.
I suggest 128 MB dictionary size and 128 bit word size as a pretty optimal LZMA2 config for compressing C2C.