There is no capital limit for Zorro S; you can set the maximum margin in the .ini file.

Although Z4 and Z5 are special strategies, the square root rule does still apply because there is no hard limit for the upper border of the EUR/USD rate. So your calculation is correct.

The backtests determine the initial capital only. The longer you traded and the more profit you made, the higher is the likeliness of a drawdown that exceeds the capital determined in the backtest - therefore the square root rule.