See benchmarking here: https://docs.google.com/spreadsheets/d/1OOwom-grrORm6C32-EM3Avk1L19z8D2AxVFKD-hNIKQ/edit#gid=0

GPU raster is quite slow on images (although oop raster is still slower than software as well).

Running at ramp@30 seconds on Linux Release, the scores were:
oop: 26.41
gpu: 14.85
software: 35.82

Somebody should take a look at this and see if there's some low hanging fruit here to fix.  This test looks like a bunch of canvases that are likely small and falling into display list canvas, and causing a bunch of raster.