Uhh... let's give this another shot in the morning.

I went through last day's upload logs; on average there are ~600 uploads an hour, the peak was 1900, the negative peak around 240. (The numbers are at http://pastebin.com/raw.php?i=wmBRJm1G in case anybody finds them useful.) So that's around 4 files per minute in worst case.

If we are aiming for no more than 10% of Special:NewFiles to be taken up by GWToolset, that means 5 uploads per run of the control job (10% of the 50 slots at Special:NewFiles) - the upload jobs can't really be throttled, so we must make sure they come in small enough chunks, no matter how much delay there is between the chunks). Also, we want to keep below 10% of the total Commons upload rate - that means 24 images per hour, which is roughly five runs of the control job per hour.

So the correct config is

GWToolset\Config::$mediafile_job_throttle_default = 5;

$wgJobBackoffThrottling['gwtoolsetUploadMetadataJob'] = 5 / 3600;

I'm leaving the max throttle at 20 so that people who are uploading small, non-TIFF images can get a somewhat higher speed.