I just loaded 6.6 and my cache is constantly hitting zero. I also noticed it wiped my unrar path during the upgrade. I fixed that so it unrars to a different drive but my cache is to 500 and it keeps hitting 155 while just downloading and when an unrar kicks in it goes to zero. I changed nothing in my hardware, this was just a 6.6 newsbin update.
Hardware is a Core i7 4790 Asus Z97 M/B with 16GB of ram.