Yeah, do what they said.
I believe people have gotten down into the 11's on the stock CCHE. From what I've read, the ATR seemed to be a lot of money for a little improvement.
Also, ATF and water/antifreeze are two very different substances. While tranny coolers will work as CCHEs, heater cores seem to work very well. They are designed for antifreeze, and their smaller size allows them to be placed in some odd locations, especially with fans on them. I believe Daron has/had Suburban heater cores mounted where the foglights were...