The best performance improvements out of tuning the Btrfs mount options came from using "nodatacow" and LZO compression. Using nodatacow is potentially unsafe since it's not doing copy-on-write for new data, so if something goes wrong you may only have a partial file to recover. With the LZO compression, the results are impressive while it can be regarded as a "safe" tunable and should work out fine for most any users with semi-recent hardware where the CPU wouldn't be taxed with the file-system compression/decompression work.