We only name a select few strains with a number. Until now we only had B.I.G. #3 . Seven is a very popular/lucky number for top quarterbacks,  winning rolls of the dice and hitting a jackpot! 
When we mated two of the most legendary strains ever known the result is the same....winner, winner, winner! "Hard work work makes for good luck" (Chimese proverb) We did all the hard work aquiring these genetics and bringing these two Hall of Famers together! Lucky you!!
Same breeds same is the logic, a simple rule of thumb for breeding. Tall x tall=tall
sweet x sweet= sweet
frosty x frosty= frosty
It's an easy, safe way to make predictable expressions of traits. Almost the very oppsite of breeding true hybrids which parent plants are extremely different. Both MW and RKS have very similar traits, fat buds, very resinous, dense poddy buds, very pungent on the stinky side, very powerful/potent and both have tendencies to add color (purples) in late flower or late seson (coldness). 
#7 will be on your starting lineup, it's a sure bet! The road to Hana is beautiful and magestic but  it is also rough as many a traveler has learned. Four wheel drive is reccomended! That describes #7 perfectly...beautiful yet dangerously hardcore! A must for all growers!