Here are some specifics on how Keyscape performs on my system.
I have an i7-3770 with 16GB RAM. C: is an Samsung 850, but I had to load the STEAM folder on D:, which is a 2TB 7200RPM Toshiba drive. (Spectrasonics recommends putting it on an SSD.) In Keyscape, I have Mode=Streamed (the default) and Pre-Load Memory Size=50,000 samples, which is about 1/3 from the bottom of the range (also the default). I've left Stream Brake (which "balances system resources between streaming and other operations") at the default 0.16 secs.
The first Yamaha C7 model takes 44-56 secs to load. With Thinning turned on, that's 17-40 secs.
The first Rhodes takes 41 model secs to load. With Thinning on, that's 28 secs.
Notes:
In each case during loading, the progress bar changes from "Please Wait" to "Preview Ready" in 1-3 seconds. I can start playing at that point.
CPU usage is low -- lower than most of my soft synths.