But it isn't, really. If you want to trade compression for speed, the presets listed on the top of the help page are far more effective.

subq=6 Default is 7. This makes compression worse.

partitions=all Higher than the default, but for negligible gain. This is only enabled on the slowest presets.

8x8dct The default.

me=umh Higher than the default, for small gain.

frameref=5 Default is 3; 5 gives small gain.

bframes=3 The default.

b_pyramid=normal The default.

weight_b The default.