A "R'G'B' u8" buffer nicely demonstrates all the aspects of the fast
paths - the buffer shifting trick and avoiding Babl format conversions.
eg., on a Intel Core i7 it gives a throughput of more than 8000 MB/s,
and if (needless) Babl conversions are introduced it drops to 1300 to
1400 MB/s.

On the other hand, a "RGBA float" buffer always performs at 1200 to
1300 MB/s, whether we avoid the Babl conversions or not. Presumably,
this is because converting "RGBA float" pixels to "RaGaBaA float" is
as fast as a NOP.

(The general fall in performance of "RGBA float" buffers is simply
because they have more bytes than their "R'G'B' u8" counterparts.)

https://bugzilla.gnome.org/show_bug.cgi?id=759616