The only thing that makes sense to me is that the HDMI cable is causing interference on the Wifi signal. Have you tried a different HDMI cable with better shielding? When I first read this I thought it would be crazy if it works, I have read many articles about all HDMI being the same ... guess tha...

I have recently bought a pi 3 starter kit ( http://www.mcmelectronics.com/product/RASPBERRY-PI-83-16561RK-/83-16561RK ) and am having severe wifi speed issues. The problem is: use of hdmi causes the wifi speed to drop significantly. Basically when theres updates to the screen wifi speed drops and wh...