EXT4 had its first win in today's testing when measuring the 2GB write performance with IOzone. EXT4 had an average write speed of 63MB/s while Btrfs was at 32MB/s and using the transparent compression support was to no advantage.
Btrfs still fell to EXT4 in IOzone when looking at the 2GB read performance, but Btrfs with transparent compression blasted ahead to win. Enabling compression improved the read speed by 2.2x and was 1.6x faster than EXT4.
When quadrupling the IOzone test size to 8GB, EXT4 still was twice as fast as Btrfs for the write performance.