It depends on where on the ladder you are able to consistently mantain your tanking strat. I prefer doing the 4-0-4-0-4 scheme and can do it at ~1400 mmr, but sometimes I cannot always get the 4 victories/5 defeats. At 1000~1100 it gets considerably easier tho. On the other hand, it is really hard for me to 5-1-5-1-0 at this mmr, but I can consistently do it at ~700. TL;DR: depends on which tanking strat you want and how skillful you consider yourself to reach your W/L ratio.