Do you want to feel that the application you're using is generally slow or slow for the actions that one could expect to take a long time to execute..?
I would like to compare it to two different real world examples.
- If the bus is always late, you can adjust your schedule/timing so that you're right on time even though it's always late. You as a user of the bus is unaffected, because you can adjust.
However, the bus runs its own schedule, unaffected by any input from the commuters. So even though it could work in a bus scenario, it doesn't apply to a user interaction scenario.
Instead think of it as what it is, a request and a response.
- If you order food from a restaurant, do you want the quick dishes to be prepared and served in the time they take to make? Or do you want the time to be consistent for all dishes, ie the quickest dishes are served in the same time as the advanced dishes? If you ordered a plate of fries, do you want it to take the same time as if you ordered a sea basket?
Sure, if you're a party you would prefer if everyone gets served at the same time, but that has more to do with a code of conduct and is not very applicable here. If you order something fast by yourself you want that damn food to be served when it's done, not to be delayed as if someone you were with ordered the most advanced dish on the menu.
I would argue a user of an application is the same, at least I am. I realize a customized search for items takes time to perform, and that's OK. However, when I view an item in the search and then go back to the search results I don't want to wait the same time again as it took for the initial search. As a user I would feel, -Hell, there's no need for this to take this long?! Why is it doing this to me?!
So keep execution times to the actual time an individual action takes to execute, no need for unnecessary waiting.