How to Set Scrapy Auto_Throttle Settings
Auto_throttle is specifically designed so that you don't manually adjust DOWNLOAD_DELAY. Setting the DOWNLOAD_DELAY to some number will set an lower bound, meaning your AUTO_THROTTLE will not go faster than the number set in DOWNLOAD_DELAY. Since this is not what you want, your best bet would be to set AUTO_THROTTLE to all spiders except for the one you want to go faster, and manually set DOWNLOAD_DELAY for just that one spider without AUTO_THROTTLE to achieve whatever efficiency you desire.
My use case is this: I have 10 spiders and the AUTO_THROTTLE_ENABLED setting is set to True, globally. The problem is that for one of the spiders the runtime WITHOUT auto-throttling is 4 days, but the runtime WITH auto-throttling is 40 days... 
I would like to find a balance and make the spider run in 15 days (3x the original amount). I've been reading through the scrapy documentation this morning but the whole thing has confused me quite a bit. Can anyone tell me how to keep auto-throttle enabled globally, and just turn down the amount to which it throttles?