Hi, rahlquist,
there is a table about apu3 PCIe slots and their usage:
J16 (mPCIe1) | USB, PCIe | USB and Wifi modules |
J15 (mPCIe2) | USB, SIM1 | only LTE modules |
J14 (mPCIe3/mSATA) | mSATA, USB, SIM2 | mSATA disks and LTE modules |
About mPCIe speed you’re right - mini PCI-e equates to PCI-e x1 2.0. Hope it'll help!