I've been playing with the read cache feature and have an EXT3 case right now where I'm saving data from the clone to an NTFS formatted USB 3 drive.
Default read cache: Up and down between 50KB and 5MB/second
Read cache of 1M: Between 50MB and 90MB/second
I should have the 300GB of data saved to the destination drive faster than the time it takes for R-Studio to load the file tree.