The next day I got my laptop, I replaced the 24GB 1600 MHz RAM it came with and put my Kingston HyperX 1866 MHz 32 GB RAM and just to confirm, been running it like this for 3 days it's perfect so it is compatible with faster RAM.
I got the hint that it would work since online retailers such as XOTIC PC and Powernotebooks also list this 1866 MHz RAM as an optional update so I'm sure they must've tested it.
Laptop has never been snappier now running all @ Dual Channel @ 1866 MHz :cool:
ALIENWARE 18 LaptopCPU: Intel Core i7-4900MQ CPU @ 3.8 GHz (8MB Cache)
Graphics: Dual GeForce GTX 780M SLI 2x4 GB GDDR5 RAM
Sound: Realtek ALC668 HD Audio with Klipsch Speakers
Memory: 32 GB Kingston HyperX 1866 MHz DDR3 PC3-14900 RAM
Storage: Samsung 850 PRO 256 GB SSD + Samsung 850 PRO 1 TB SSD + Samsung 840 EVO 1 TB mSATA SSD
Screen: Samsung LTM184HL01 18.4" WLED FHD (1920 X 1080) TrueLife Display PLS 16:9 1080p [SDC4C48]
OS: Windows 8.1 (x64)