I've found that manually adding to Preload Size in the Database does nothing significant in terms of relieving CPU workload on playback.
My total RAM use is well within my machine's maximum (64GB).
In my Synchron orchestra stress tests, the iMac's Activity Monitor shows no noticeable fetching of samples from storage during playback, either with or without my additions to Preload Size.
Of course the hugely critical factor in CPU streaming workload is how many mix channels are switched on in the Synchron Players. To get an idea of how well or badly my system performs under various conditions, I've been experimenting with a Synchron basic symphony orchestra under various different levels of stress. This test build in Logic doesn't use VEP; there are no plugin Fx running in the Synchron Players or in Logic; and just 2 stereo audio routes between each Synchron Player and Logic.
Stress testing the whole of this basic orchestra (27 Synchron Players) consists of running a looped 1 Bar chromatic scale of nearly 2 octaves for every Synchron Player, every note a 1/16, played as fast legato at various different BPMs and with various numbers of Synchron Player mix channels switched on.
At my fastest sensible tempo of 110 BPM and with only 1 mix channel switched on in all players, I get this:-
With 4 mix channels switched on in all players, at the same tempo, this:-
No audio plop-outs and no CPU crunch-outs anywhere.
Not too shabby for a 2017 iMac 7700K - helped along by recent addition of a couple of very fast Samsung SSDs via Thunderbolt 3.