Dudechris's issues I don't think are frame rate related though. Been working through his thing in a separate thread.
S2imon, I haven't see any frame rate slowdown's myself. The default delay I set in PNG Animator is 0.04 seconds per frame. Granted thats not 30fps, tad slower, but sometimes I'll use 0.03 or 0.02 and I haven't noticed a problem. If you aren't using that program, to give you an idea...
30fps would be 1/30 so 0.033 for the time per frame
60fps would be 1/60 so 0.016 for the time per frame
One of my packs uses a lot of really high frame rates because I wanted the stickers to look a bit crazy / jittery. If you search Espresso Stickers you can see what I mean. Its free.
What kind of device are you guys testing on. I use a 6 Plus. Maybe on some of the older ones the crashing could be explained by the device.