Since I have a laptop instead of my desktop PC I have wondered why the laptop was twice as slow as my older desktop. Both have an Intel i7 processor and loads of memory, but when I click on a photo in Lightroom to 100 % viewing it takes 10 seconds on my laptop instead of 5 on my desktop. Finally found what caused it! In the Power Options, Advanced settings there's the minimum processor state and it's set at 5 % by default. I've cranked it up to 100 % and now Lightroom and other stuff runs as fast as on my desktop. I also set the System cooling policy to active. More explanation here; it's for Windows 7 but my Windows 8.1 installation shows these same features.