Okay, reflashed this firmware, did full factory reset on both nodes, and now everything's copesthetic *smile*. Speed is fine, everything's running well.
Personally, I don't worry about the amount of free storage that a Linux-based system shows, as long as it's performing well. It's been characteristic of Linux to allocate as much memory to program images and buffers as possible, often showing 100% memory usage, and reclaims what it needs from currently unused space when something comes along that pushes it over the edge. That helps in not having to reload code modules when re-invoked, or re-fill buffers that are already ready, kind of "lazy" memory management that makes things run faster in the big picture. Not like your classic UNIX, but works really well.