What nitro content are you running? The higher the nitro and/or humidity, the "cooler" the plug you should use. I ran OS hot plugs when I first started and found they burnt out quickly. The DP medium's have lasted about 3 times as long here in Florida. I'm planning to switch to the O'Donnell 99t (cold) when these run out in hopes of getting longer life in addition to the cost savings.

I should probably mention that the plug "temps" aren't necessarily comparable between manufacturers.