The only setting that I've found having significant effect is /dcc packetsize 512
You can try any value between 512 and 8192, most people say they have the best success with 512.

Note that DCC is a horrible protocol for file sending, and a more suitable protocol such as FTP (File Transfer Protocol) will yield better results.

- Raccoon

Well. At least I won lunch.
Good philosophy, see good in bad, I like!