Which Tremec TKX Do I Get

I've decided that the 2.87 TKX 1st gear may be best for my combination. With 3.55's and 27560R15 tires, I cruise 60mph@2500-2600. Motor makes 465ft;lbs@3000, peaked 510ft;lbs@3900. Car weighs 3400 with me in it. Now, which OD do I get? .81 or .68? Pros & cons?