The performance difference will be negligent, since the system is already bottle-necked by the CPU and the amount of memory. I would not worry about it.
Thanks for your answer!
The cache works by writing lots of relatively little files -- one for each frame in the comp, plus one for each frame for each layer. For example, a 10-layer, 100-frame composition can generate 1,100 cache files (one per layer per frame, plus one per frame for the comp overall).
In other words, the cache isn't just storing the composite of all layers together; it's saving that, plus the internal composite of each layer individually.
That's a lot of I/O requests, so keeping the cache on an SSD is very helpful in minimizing latency, and keeping the cache separate from footage is helpful in reducing I/O requests on the same drive.
Correct to say that the read/write going on with the cache is much greater than the IO to/from the footage? are they somewhat close in IO demand when rendering? or is it "mostly" just reading the footage during the process?