A lot you have probably seen this by now, but
Chad Ryker did a review of the RT660 recently. He was able to compare to other brands of tires, but it is clearly faster than the 615+. It's still not clear yet that they have produced the 315/30/19, but he had some inside info that they did and it's on the same cargo ship as the other big sizes. Nothing shows up on DiscountTireDirect.com for that size yet, but it is still listed as a size on Falken's own site.