The prey, no matter what it is should never be bigger then the body of the tarantula not including the legs. I personally would never feed a mouse again to any of of my 112 tarantulas. We feed pinkies to 4 of our tarantulas and 2 died. The place that we got them at we figured had used mite spray either on the pinkies or in the container. It was fairly quick how fast the poison worked on the tarantulas. Within mins the spiders where in a death curl.
I also agree that it is too much calcium for a tarantula if fed a constant diet of mice.