Tention with a 3 or 5:1 works well, with a GCRS or vehicle but this is the LAST option as you can measure the tension being applied accurately. Remember the side loading forces in speedlining are something to know and respect.
Speedlining is a controlled lowering system, it shouldnt be abused by cutting out pieces streight onto the main line. As Ekka says 5x yea well thats the thing, it could be 15x who knows, sure you can do testing but every single rig is different.
Just stay well within the gear, the trees capabilitys.
