Highwater's Stan's Red is a low-fire earthenware, firing range ^06 to ^02; Highwater's Red Rock is a stoneware that fires to ^6; at ^6, Red Rock is not really red, but a brown red. Stan's is a good majolica clay body (as is Highwater's Earthen Red which can be fired to ^4); I would not recommend Red Rock for majolica work (and Red Rock is one of my regular clay bodies).
For good info on majolica, including clay bodies, check out Linda Arbuckle's website. http://lindaarbuckle.com/index.html
Her handouts are a wealth of information from one of the best majolica artists around. Linda uses a custom clay body based, if I recall correctly, on Stan's Red but with a few modifications of her choosing.