Rule of thumb: When your system performs different with and without TICKS, always test with TICKS. Z1 and Z2 use TICKS for the backtest.

TICKS can make a difference when your system often uses pending trades, or when it often exits a trade with a stop or takeprofit limit. TICKS won't make much difference with systems that mostly exit trades by script.

For the backtest, you need not set the Spread - the system does this automatically. You only need to set it when you want a particular spread for some reason.