I too have noticed severe frame rate drop with the Singapore Landmarks installed. Especially when panning a direction that is not facing the CBD to panning towards it. Frame rate drops to about 20fps from a solid 60+ fps. I have CloudSurfAsia's WSSS also installed.
My Specs:
Intel i9-9900K @ 5.1ghz
RTX 2080
32GB RAM
M.2 NvME 2T SSD
Windows 10