A lower t-stat will not help all by itself under adverse condtions such as high ambient temperatures, slow vehicle speed, A/C on, racing, etc. To get the full effect from the lower t-stat you will need to get the radiator fans to come on at lower temperatures too.
There are a couple of fan mod threads on the forum. One requires only a piece of wire, otherwise no cost. Problem is the fans run continuously, even when the key is switched off! Good for drag racing, not so good for everyday use. Another uses a couple of wires and a manual switch and you're in business for about $10. For automated lower fan-on control you can use an adjustable thermoswitch for about $70. Or you can get a Diablo Sport Predator and electronically lower you fan-on temperatures (and get some performance tunes and the ability to adjust many other parameters in the process!) for about $350.