Not necessary, as it's nearly verbatim what's in the Nvidia README, and I 
managed to get this working by fixing my config file, which, admittedly, 
was a bit backwards.
(I had mistakenly thought that the intel chipset would be managing the 
screen resolution, as it's the output device- also, this is my first time 
configuring an Optimus-equipped machine).

Also, I might still want both sets of OpenGL drivers, per the askubuntu 
link, in case I want to run the intel chipset alone, on occasion.
(I'll need to see just how power and temperature-efficient this setup is, 
to determine how often I should opt for one over the other, but having the 
option, in and of itself, is a good thing, methinks.)

ANYHOW, here is the working config- I'll update the wiki this evening, as 
someone else may find this useful (should probably do the same with the 
synaptics config for my Elantech trackpad). It's working quite well, so far.


Section "ServerLayout"
  Identifier "Displays"
  Screen 0 "Internal Screen Nvidia"
  Inactive "Intel Corporation Crystal Well Integrated Graphics Controller"

EndSection

Section "Monitor"
  Identifier "Internal Display"
  Modeline "3200x1800_60.00" 491.57 3200 3448 3800 4400 1800 1801 1804 1862 
-HSync +Vsync
  Modeline "2560x1440_59.90" 311.31 2560 2744 3024 3488 1440 1441 1444 1490 
-HSync +Vsync
  Modeline "2400x1350_60.00" 273.59 2400 2568 2832 3264 1350 1351 1354 1397 
-HSync +Vsync
  Modeline "2240x1260_60.00" 237.85 2240 2400 2640 3040 1260 1261 1264 1304 
-HSync +Vsync
  Modeline "2080x1170_60.00" 203.45 2080 2216 2440 2800 1170 1171 1174 1211 
-HSync +Vsync
  Modeline "1920x1080_60.00" 172.80 1920 2040 2248 2576 1080 1081 1084 1118 
-HSync +Vsync
  Option "PreferredMode" "1920x1080_60.00"
EndSection

Section "Device"
  Identifier "NVIDIA Corporation GK104M [GeForce GTX 870M]"
  Driver "nvidia"
  BusId "PCI:1:0:0"
  Option "monitor-eDP1" "Internal Display"
#  Option "monitor-DP1" ""
#  Option "monitor-HDMI1" ""
EndSection

Section "Screen"

  Identifier "Internal Screen Nvidia"
  Device "NVIDIA Corporation GK104M [GeForce GTX 870M]"
  Monitor "Internal Display"
  DefaultDepth 24

  SubSection "Display"
    Depth 24
    Modes "3200x1800_60.00" "2560x1440_59.90" "2400x1350_60.00" 
"2240x1260_60.00" "2080x1170_60.00" "1920x1080_60.00"
  EndSubSection

  SubSection "Display"
    Depth 16
    Modes "3200x1800_60.00" "2560x1440_59.90" "2400x1350_60.00" 
"2240x1260_60.00" "2080x1170_60.00" "1920x1080_60.00"
  EndSubSection

  SubSection "Display"
    Depth 8
    Modes "3200x1800_60.00" "2560x1440_59.90" "2400x1350_60.00" 
"2240x1260_60.00" "2080x1170_60.00" "1920x1080_60.00"
  EndSubSection

  SubSection "Display"
    Depth 4
    Modes "3200x1800_60.00" "2560x1440_59.90" "2400x1350_60.00" 
"2240x1260_60.00" "2080x1170_60.00" "1920x1080_60.00"
  EndSubsection

EndSection

Section "Device"
  Identifier "Intel Corporation Crystal Well Integrated Graphics Controller"
  BusId "PCI:0:2:0"
  Driver "modesetting"
EndSection

Section "Screen"
  Identifier "Internal Screen Intel"
  Device "Intel Corporation Crystal Well Integrated Graphics Controller"
EndSection