Wagyu cattle(japanese black) are divided into 3 main strains
the bigger the animal usualy the lower the marbling. There are some exceptions, Yama beef in Texas own a bull called ITOSHUGEFUJI he is about 1100kg & is proving to be quite a performer, the other end of the scale is a bull owned by Snake River Farms FUKUTSURU 068 , & he is "a scrawney little critter"
but his carcases are exceptional. look at the website :www.blackmorewagyu.com.au
This mans wagyu cows (about 7-800) are all well over 650kg ,more like holsteins. In a conversation with him he told me that when breeding fullblood wagyu the rule of thumb was "3 crosses for size to 1 cross for marbling" to produce a practical cow that a cattleman can run without too much maintanance.
you might like to look at the Australian wagyu association web site .
regards
Tully