Boiled 7 gallons today down to a final 5 gallons for fermenting. Cut the flame off at 2:05pm, had it down to 100*F at 2:12 via a 50ft ss 3/8" immersion chiller.
For the record, I too am in deep southeast Texas where groundwater is around 85* this late in the summer.
So, after getting down to 100* in about 7-8 minutes, I switch over to a bucket of ice(about 25lbs) and water. I found a clothes hamper from Walmart that has rope handles for about $7. It's big enough to hold my 7 gallon ss brewpot perfectly. I'll mention that at around 100*, I remove the wort chiller... it just isn't going to cool any lower than +/- 100 in these temps.
My notes from today's boil/cool down show that at 2:28pm, 23 minutes after flame out, I had 70*F wort! I brewed last Tuesday, and the result was similiar... take about 10 minutes to chill down to about 100, then switch to ice bath. I'll stir my wort continually AND swirl the ice on the outside of the brewpot. My goal is to have warm wort transfering to the ice cold surrounding water constantly.
Sounds like a fair amount of work, but it's not. Having wort chilled down to 70* in less than 25 minutes in the brutal heat of the day is priceless!