I've had two sets of Avids over 3 or 4 years….so plenty of pad changes before now…but I do think the 5s are harder to push the pistons back than the 7s? Having also changed pads on a friend's Avid Juicy 5s, which required so much force to lever the pads apart that the disc brake mount was flexing, I think they can be a bit temperamental. Hayes were similar, often needing the bleed port undoing to let fluid out.
Removing the clip spring on the back of the caliper is an interesting tip though.
Still debating whether to sell them or keep and put them on the hardtail…