iPad mini 2 vs. iPad (2017) - Speed Test
Although these speed tests are useless as you can't see the real differences. The iPad 2017 is more than twice as fast as the mini 2 on the same iOS, and caches almost all the apps in RAM. What I find disturbing is the mini's standard functions, like turning the page in iBooks have been slowed down over the last few versions, which does not require too much resources.
You should wait before upgrading to iOS11 on iPhone 5S and iPad mini 2, until you read some positive feedbacks. I will probably upgrade and do some speed tests on it too.