Maximum GPU Upgrade for m18xR1

Nvidia: GTX 780m / GTX 880m.

AMD: HD 8970m / R9 m290x.

Thank you for the response about the GPU.  Which vendors are recommended  for sourcing this GPU and the other parts needed for an upgrade?

• You probably have the 3-pipe heatsinks (I think they come standard in the m18x / 18), so all you would need for extra is thermal paste and thermal pads, both of which are cheap to acquire. Some upgrades do require either a modded vBIOS and modded driver, both of which can be acquired in notebookreview's forum or techinferno's forum (under the Alienware section).
• As for the GPU, ebay, rjtech, eurcom, some forum, etc. Mobile GPUs are harder to acquire compared to desktop GPUs.

I found the Eurocom website, which seems to sell everything needed for the upgrade. 

However, I am now wondering if it's better to get an 880m or two 860m cards for SLI.  Does anyone have any good info about the tradeoffs?

The 880m has some thermal problems, so I would get a GTX 780m. As well, they're both the same GPU, so you could overclock the GTX 780m to match the GTX 880m.

That, and since VRAM doesn't stack in SLI, it might be best to get a single GPU with a good amount of VRAM. That way, you can get the same GPU later for a cheaper price.

Otherwise, you'll be getting similar performance.