IMatch by default uses the default storage location for application data as defined by Windows.
IMatch uses advanced caching in-memory mechanisms when working with cache files, as well as for the database. During normal operation, when
using the cache, you won't notice much of a difference.
But having the database and cache on different disks while
indexing thousands of files should gain some speed. IMatch writes to the database and to the cache files simultaneously and from multiple CPU threads. The amount of data transferred per second is high during this stage. If the load can be distributed over two disks, there should be a noticeable (but small) performance gain. All this depends of course on multiple factors, like how much RAM is available for the Windows disk cache, processor speed vs. disk speed, if you use regular hard disks or SSD's etc.
In short: Try it out and let us know

We're all learning new stuff about IMatch 5 all the time...