As many times as I've tried the 42mm Explorer on the wrist, I find it huge in comparison to the SubC which is a perfect size on my 7.5inch wrist. And that is coming from someone who's used to large watches, 45mm Seawolf's, etc. It sits very flat and with the stainless bezel it probably appears larger in diameter than the size suggests.
The 8500 PO is a proper fatty, and sits really high, almost 20mm in thickness. As lovely a watch that it is, I much prefer the slimmer form factor of the older model, but would miss the excellent in-house movement.
Neither would be my choice, I'd sooner go for a 114060/116610 Sub or 116710 GMT, but of the two you've suggested, the Explorer wins it for me.