do you have a link for the dummy plug?
many thanks.
there is one from amazon :
https://www.amazon.com/gp/product/B00FLZXGJ6/ref=oh_aui_detailpage_o08_s00?ie=UTF8&psc=1and one from ebay :
http://www.ebay.com/itm/191567271934?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AITyou dont need a dummy plug if you have a monitor attached to any of your rx 480 , and the monitor is turned on all the time.
you need a dummy plug if you are running a headless system , (no monitor attached to your computer , or if the monitor is not on during mining) and remotely controlling your setup , via remote desktop teamviewer ...
[Apologies if this has been addressed. If it has, I could not find it.]
*Two RX480 GPUs, detected and working on Win7.
*16GB RAM; SSD; ASUS P8Z77M mobo.
*Intel HD Graphics 4000 driver onboard video driver is active.
*Both use their own 750W PSU.
*Latest AMD driver (16.11.4) on both.
Using Claymore Dual ETH v7.2.
Claymore sees both Ellsmere GPUs fine. Mining function works as expected. But one GPU mines at ˜22MH/s, the other at ˜4MH/s.
"Both use their own 750W PSU"Why are You using 2 x 750 watts psu for 2 x rx 480 setup
you should run your setup from 1 750 watts psu with 2 rx 480 card without any problem !
"one GPU mines at ˜22MH/s, the other at ˜4MH/s"
22MH/s is to low for the stock rx 480 , there is probably some driver or i/o conflict in your system that is why you get 4MH/s on the second card . Or you are using a wrong modded, flashed bios for your RX 480's
[Apologies if this has been addressed. If it has, I could not find it.]
How might I get GPU1 to perform as well as GPU0?
1st :
-
use 1 psu !!!- plug one of your RX 480 on the first pcie 16X slot , connect your monitor for the same card , (the longest blue one close to the cpu) via powered usb riser , leave the second one unplugged
- go to your bios settings and disable on board graphic
"Intel HD Graphics 4000 driver onboard video driver is active."
- boot into windows 7
- dowload DDU (Display Driver Uninstaller )from here : http://www.wagnardmobile.com/?q=display-driver-uninstaller-ddu-
- run DDU , option restart the pc in safe mode to remove the drivers .. remove all amd and intel drivers , reboot .
- after reboot install the latest AMD driver , still only one of your rx 480 plugged in via powered riser http://support.amd.com/en-us/download
- reboot .. wait till windows recognize and assign the driver to your card.
- turn of your pc , connect the second rx 480 via powered usb riser to your computer , use the second slot on your motherboard ( pciexpress , blue 2nd from the cpu)
- turn on your pc , and wait wait wait , windows sometimes need 5-10 minutes to assign the driver for your second card during this time your monitor screen maybe go dark going to flickering , dont Be panic , just wait .... just in case leave your pc running after reboot for a 5-10 minutes windows maybe working in the backround assigning the driver .
- reboot , set virtual memory at least 16GB on your system http://www.online-tech-tips.com/computer-tips/simple-ways-to-increase-your-computers-performace-configuring-the-paging-file/
- reboot , use latest claymore miners for ETH or Zcash
- make sure you place this into your start batch file :
GPU_FORCE_64BIT_PTR 0
GPU_MAX_HEAP_SIZE 100
GPU_USE_SYNC_OBJECTS 1
GPU_MAX_ALLOC_PERCENT 100
GPU_SINGLE_ALLOC_PERCENT 100
2nd:
If the first steps did not worked for you , i would suggest a fresh win 7 install , and follow the steps above except the Display Driver Uninstaller parts 
