who will win?...

5703615 40K. Superior technology, swarming hordes, reproduce by dying and spreading spores, generally much stronger and more blood thirsty than an average human.

5703656 What he said.

5703656 As much as I'd want Thrall and the horde to win, yeah. 40K.

5703615
If this were fantasy then maybe the Horde. Sadly this is 40k.

Now if the Warcraft orcs had starcraft tech this might be a different story.

Generally any 40k vs _____ situation/thread will almost always have 40k win in a curbstomp due to the sheer scale and over-the-topness 40k has. So Orks.