I keep seeing people recommend slowing the water flow to improve efficiency or speed or something. It's just not true. Period. End O' Story. Thermal transfer is higher with greater temperature differential, so the colder the water and the higher the volume flow rate the better. Always.
I'll almost guarantee that the OP just dunked his chiller in the kettle, turned on the water, then kicked back and waited. My well runs around 55°F this time of year and I used my IC last brew day (usually use a PC) and cooled a full 5.5 gallons from boiling to 66°F in 8 minutes by simply keeping the wort spinning the whole time.
It takes literally just two seconds of not stirring to feel the "out" water from the IC get hotter than if you keep the wort spinning. That should tell you all you need to know...
Cheers!