I think processor power and RAM both help. I recently started a new game with the 1.03 patch and some new hardware and turns take <1minute to resolve, whereas before it took about 5 mins. I think AI wars seem to really slow things down, so if you get a twenty year war between Russia and Japan, for example, maybe you should take control of them and make peace (Taiping rebellion notwithstanding). I find that if turns take less than a couple of minutes then I can sit through them.
