I have pretty decent hardware and I run many games on it. But Civ 5 is unacceptably slow when it reaches an advanced stage where it shows the whole map and there are many units.
I tried to monitor the CPU and memory and I couldn't find the bottleneck. I run it in a fast SSD and I didn't monitor my GPU.
I noticed a speed improvement when I changed from DX10/11 to DX9. But the performance isn't acceptable yet.