Was able to hear 1660 when it was WCNZ in Sep 2004 doing daytime DXing from Port Fourchon, LA. Clearly? Absolutely not. But considering how high on the dial they were, I figure that to be a nice catch.
From that spot, was able to hear Cuba (670 & 710 IIRC), KVNS 1700 TX, and XEFW (even harder to catch than WCNZ) Tampico. I'd say that those were the "extremes." So that's about a 900 mile swath, Gulf wide!
cd