I have tried to optimize website for speed by decreasing active plugins, optimizing caching, etc, and while it worked to get it down to around 2.5 seconds for which I was really pleased, its not consistent however. Say I do 10 tests, the speed would range from 2.5 to 7 seconds. Twice I got 2.5 seconds, several times just over 4 and twice over 7. I did it a second time around 8 or 9 tests and the same thing.
I think I have to use content delivery network (CDN) to serve images. I think that's what will make the big difference.