I cached a region going ~25 miles west from KJFK into NJ and ~10 miles high (above the upper tip of Manhattan) in high detail. It took me about 1 hour to select and add the small high details squares to my desired named cache and it took over two hours to download the 45 Gb with my CPU and GPU cranking away the whole time. A theory espoused in the following thread is that the raw data from MS is being processed into FS form during the download (to spare MS the server/electricity cost of processing huge amounts of data for all the many, many people using MSFS). #1: The Manual Cache Should Be Redesigned From the Ground Up, Possibly Connecting Designing a Flight Plan With Manual Caching if Desired - #4 by DumpofDeath22
I didn’t find that having all this high detail data of the area around Manhattan really improved my FPS at all. My unproved theory is that there is SO MUCH detail to display in the buildings around Manhattan with all the lighting and reflections between buildings, etc., that even having all the structural/textual data, your computer is still terribly bogged down given your aircraft’s altitude, heading, speed, etc., doing the calculations as to exactly what to display to you on the screen in the very, very complex scene that Manhattan represents.
The other thing is that once you have created a manual cache of any size, if you go to view it, watch out! #2: The Manual Cache Should Be Redesigned From the Ground Up, Possibly Connecting Designing a Flight Plan With Manual Caching if Desired - #22 by JALxml