@airsick
Why would you say that CTC responding slowest means they don't care? Perhaps they would rather take the time to select the right candidates rather than sending everyone for assessment (and making more money out of people who have no chance?)
Personally, I would be much less happy if, after spending hours and hours on my application, I got an email inviting me for assessment within hours. That would imply to me that they had not even been given a cursory glance and were just inviting everyone who applied to line their pockets with the selection fees!