Another episode of "trying to do things that weren't meant to be done"...
I was wrong about it switching back to SG, it stayed on PEG. I tried a few more things today and will just summarize from the beginning here:
I have an Alienware M17x R3 with an AMD HD6870M. I got a Dell R9 M290X to replace the 6870. BIOS was set to PEG upon starting procedure.
1) Swapped thermal solution to new card & installed new card
2) Powered on, got black screen
3) Powered off, removed CMOS battery
4) Powered back on, got black screen & 8 beeps
5) Powered off & on a few times, same results
6) CTRL+ALT+DEL, rebooted, same results
7) Removed new GPU
8) Booted fine with no discrete GPU
9) Checked BIOS, was still set to PEG
10) Set BIOS to SG
11) Reinstalled new GPU
12) New GPU shows in BIOS - ATI GFX
13) New GPU shows in Device Manager - AMD Radeon HD8970M
14) Intel GFX driver had a bang - Code 31 could not load drivers
15) Rebooted, same results
16) I'm using the Dell Intel driver - 8.15.10.2342 (it's old, but it allowed me to use HDMI-In with the old card)
17) Rebooted, now both cards have bangs
18) New card's driver says Code 12 cannot find enough free resources
19) Tried to auto update drivers, same results
20) Uninstalled both devices from Device Manager
21) Rebooted
22) Both showed up under Other Devices with no drivers
23) Reloaded drivers, Intel driver works, but same results with AMD driver
34) Had read somewhere that the integrated audio might interfere with some of these cards, so I tried disabling the onboad audio in BIOS, same results
35) Listed devices by connection in Device Manager, saw that AMD High Definition Audio Bus was on same controller, so tried uninstalling that, same results after reboot
36) Enabled show hidden devices in Device Manager, saw old 6800 series driver still there, but showing disconnected
37) Uninstalled old card's driver, rebooted, same results
38) Ran GPU-Z, shows vBIOS 015.046.000.014.045579
39) GPU-Z did not show any sensor data
40) Ran HWInfo, shows GPU fan at 35%, but I have not seen the fan come on at all
38) Set back to PEG in BIOS
39) No black screen this time, was able to see the OpROM screen for RAID controller
40) Right after that, got corruption/artifacts on the screen (several vertical blue lines with some scrambled looking text)
Suspect the artifacts/corruption might be due to heat, since the fan does not seem to be working. Will let it cool off and try again later.
Here's some info on the resource usage shown in Device Manager:
HD8970M - PCI bus 1, device 0, function 0
I/O - 0000000000006000-00000000000060FF
Memory - 00000000A0000000-00000000AFFFFFFF & 00000000C8400000-00000000C843FFFF
IRQ - (PCI) 0x00000007