Hey Mega,
Hopefully you have your event sheets sorted out and have things placed into groups, if so the profile view will show you how much of your cpu is being taken up by each group. Look for the big %'s first, does it make sense that X group is using that much?
Can things be optimised in that folder? When you disable groups of code does the fps spike up?
You are right that there is no safe values due to the wildly dif specs of devices, you just want to keep things as low as possible on what you have.
Things that will likely be killing your performance are unnecessary everytick events.
If everything is fairly optimised code-wise, see how things go when you strip out some assets. Could be you are getting gpu bottlenecked.