Wow, here in UK we change Oil every 10,000 miles, both for RX-300 and Ford Explorer. We have no extreme temperatures. Lowest say 20 F and highest 80 F with mean average 60 F.
Oil is meant to have been improved over the years. My RX-300 is a Japanese Import and the car is covered in Japanese under the bonnet (hood) and it says 10,000 kilometres which is 6,250 miles. So 7,500 sounds OK, 5,000 a bit paranoid?
Best of Luck
Nick