I think the answer to my puzzlement is that there are 2 different buffers going on, a file-system buffer that has to do with reading data off my disk, and another buffer that has something to do with my soundcard.  Maybe.
 
When I'm tracking, I set my AtoD hardware interface buffer size to 128, and I don't experience any latency issues, at least any I can detect.  When I'm done tracking and moving on to mixing I set the hardware interface buffer size to 1024, as otherwise Melodyne will complain, and raising that seems to give me more cpu headroom to run Prochannel stuff and various cpu-hungry plugins.
 
However, to confuse me, on the Preferences/Sync-and-Caching tab there is a playback and record buffer size which are both set at 512kb for like forever, as in like a decade or more.
 
These things don't seem to need to agree with each other, methinks, but it does puzzle me enough to post.

All intended to buffer different I/O.
Don't forget the MIDI buffer too!
 
Interface - Number of samples buffered going in and out of interface.
Playback/Record - Data buffered for disk reads and writes.
MIDI - Memory set aside to buffer MIDI data.
 
At least that's the way I see it. Someone else may correct me.
 

You are using the sample buffer correctly.
The Disk buffers you can leave at default usually.
The MIDI prepare buffer you should change to 750 or 1000
This used to default to 500 but in Platinum defaults to 250.
I always had issues even at 500 with dropped MIDI drum hits so I set it to 1000.

has anyone changed any of their disk buffer settings?  I had an instance of where my playback on WMP and any other playback devices had random, intermittent pops... drove me nuts.  I re-rendered files, changed buffer settings, analyzed waveforms but nothing was visible in the waveform,  then I finally figured out it was the playback where it occurred.  I figured it must have been related to the sound card and buffer setting,  but never thought it would happen in playback outside of the DAW.