I'm having two performance issues which appear to be closely related.

The first is the white tactical combat screen, symptoms of which appear to have been amply described already.  This occurs every time playing at full-screen: 1920x1080.  It is possible to auto-resolve the combat, but when this is done the game's graphical performance sharply declines to the point of being so slow as to be unplayable.

http://filebin.ca/tuwxcm/DebugFullscreen.err

This can be more or less worked-around by running in a window at a lower resolution.  But a similar problem appears eventually.  I can play a seemingly random number of tactical battles (1-4ish) without issue, but eventually one causes the game's graphical performance to sharply decline.  This occurs at the beginning of a tactical battle and persists after the battle is fought or auto-resolved.  While in this case the tactical map is present, the manner of the slowdown is similar to the first issue with the white tactics map.

http://filebin.ca/jqnqd/DebugWindowed.err

Both fill up the Debug Log with an endless repetition of similar error messages:

Debug Message:  ERROR: (CD3D9Renderer) Unable to create a depth stencil surface in ::CreateDepthStencilSurface.
Debug Message:  CDXSASTexture ERROR: Failed to create depth stencil surface
Debug Message:  CDXSASTexture ERROR: InitTargets failed for parameter: DepthBuffer
Debug Message:  CDXSASEffect ERROR: Could not initialize texture from the parameter: DepthBuffer
Debug Message:  CDXSASEffect ERROR: Init failed while loading texture information

One thing I did note is that there do not appear to be a fixed number of iterations of this error message.  Once the game has produced this error message it will continue to do so in a loop as long as the game is running.