I had been using SampleTank 3 periodically in the past, and a few days ago installed ST4 Max which I use as a plug-in with Pro Tools 2018.4. I was getting frustrated as ST4 was freezing and crashing Pro Tools when I was using the C7 Grand Close Mic Natural piano instrument (which is about 11 GB in size) or the other large size instruments, even though it was the only track instantiated.
I had my computer built for me three years ago which has a MSI X99A SLI Plus LGA2011 motherboard, i7 5930 3.5 GHZ 6 core 12 thread CPU, Kingston HyperX Fury 64GB DDR4 2400MHZ RAM, NVIDIA Quadro K2200 GPU, Samsung 850 Pro 512 GB SSD for OS, and a Western Digital Caviar Black 1TB SATA III 6Gb/s 7,200 RPM hard drive for the ST4 and ST3 samples, and a separate one for audio. The audio interface is a RME Fireface UFX with USB2 connection.
The hardware buffer size was set to 128 samples which I had previously used in Pro Tools with ST3 and other virtual instruments without problems. However, with ST4 and large instruments like the C7 Grand, the System Usage Meter in Pro Tools showed that the CPU meter was spiking from around 30% to near 100% even without playing it. When I was playing it, Pro Tools would seize up periodically. If I was using a ST4 instrument like the Tonewood Pipe Organ which was less than 1 GB in size it was fine. I then raised the hardware buffer to 256 samples which was better, but still occasionally froze Pro Tools when playing the C7 Grand. I tried changing various parameters in PT and ST4 but that didn't seem to help.
Yesterday, I had the Samsung 970 EVO Plus M.2 NVMe 1 TB SSD installed in my computer, then I moved my ST4 samples to it from the Western Digital HDD. While I have only been testing it for a brief period, it has been working fine so far. The instruments load almost immediately into ST4, and I've had no freezing or crashes in Pro Tools. The CPU meter in PT shows an average of about 30-50% with occasional spikes to around 75%. I've left the hardware buffer at 256 samples as I have not noticed any latency when playing the keyboard. I will do more testing at a later date with other virtual instruments loaded and audio tracks playing, and hopefully it will still be stable.
I have read some other threads in this forum with people experiencing CPU spikes and freezing of their DAW while using ST4. I did not expect that myself as I thought that with 64 GB of RAM and a relatively fast CPU & GPU that I shouldn't have any difficulties. However, it appears that the HDD was not adequate with large instruments in ST4. Hopefully, this information might prove helpful for anyone else encountering similar issues.
As a further note, I have found some great sounding instruments so far (pianos, organs & pads) in ST4 with some brief exploring.