I have an i5 2500k, 4GB ram DDR3 and a GT1030 and I have 50+ FPS in Montgomery, which are lower than the average 90's I get. I didn't say you have LAG, you have lower framerate.You are totally wrong. I have a low end laptop (I could say) and my fps in Montgomery are totally fine. Mention: I got a damn 1.9GHz Processor, 8GB ram DDR3 and a 2GB ram DDR3 GPU. If you have low fps in Montgomery I suggest you to close some background programs. This helps a lot.
Try comparing your framerate when you're out of Montgomery and when you're in Montgomery.