Actually only RAM (2 vs 3 GB) and internal memory (8 vs 16 GB).

However, USB might be the most limiting. You can't attach a webcam or USB gamepad to it.

The internal memory should be sufficient for the Plex cache (icons, fanart...), but could be swapped out to the SD card, which you should make sure is fast. For me, an XC Class 1 with about 10 MB/s write only worked to a limited extent, as it slowed everything down (not tested with Plex, but other apps).