Upload & Sell: Off
Looks like a significant upgrade over the older E-P3 (which was arguably inferior to the cheaper E-PLx models)
1. 1/8000 max shutter
2. 1/320 or 1/250 flash sync (1/250 with shoe-mount flashes, 1/320 with the popup, hopefully that includes with the popup as a commander)
3. ISO 100
As well as the little incidentals.
Same battery as E-M5
VF-4 finder, which is much larger and higher-resolution than the already good VF-2/E-M5 finder
Better control layout
Essentially the E-P5 is an E-M5 with a detachable finder (and the pricing reflects that, it basically straddles the E-M5 in cost with or without the finder).
The only downsides I see are no weather sealing and it's incompatible with the E-M5's grip.
As to the lineup, it is:
OM-D E-M5 - Sealed, SLR-alike, most flexible (available Grip, etc). The most enthusiast-oriented camera and the one oriented towards 4/3rds users (it actually handles alright with larger lenses due to the grip)
Pen E-P5 - Premium RF-style model, semi-compact with OM-D performance.
Pen E-PL5/6 - Sweet Spot consumer model - Flip screen, mid-range everywhere else
Pen E-PM2 - ultra-compact, gives up features for small size. Also the cheapest.