SpoutCam 2.036 is available with functions for rgba to rgb optimized for x2 speed gain.
rgba_to_rgb_sse3 - 2.5 msec at 1920x1080, 1 msec at 1280x720
rgba2rgbResample - 2.3 msec 1920x1080 > 1280 x 1024
Follow the download instructions for the release.