I have upped the aspect ratio to 70 on a pair of Michelin's (2012 Silver Edition).
They are probably the Defender LTX (I will check later; it is what my CostCo had).
The TL;DR? My Speedo is now correct with every GPS speed measuring device I can throw at it.
With the 265/65/r17, 70 MPH indicated was actually closer to 67.
I am nerdily giddy about this.