Never flown a 5m yet. My setup is to have exactly equal lines and exactly equal pigtails on the 2 centers the 2 rears and the 5th line. Then on the end of the 5th line I lark's head some q-powerline and make knots at the above distances. Then I lark's head my 5th line pigtail on to the corresponding knot. My goal is to have exactly 90cm of slack in the line. I think the numbers are correct, if I got my measurements wrong I'll go back later and fix them. I don't ever have a ruler of 90mm out at the launch but my palm is 90mm (3.5 inches) and I use that to measure the slack. Up to 6 inches (150mm) of slack is ok too but you can't go below 3.5 inches (90mm) or the kite starts to pinch.
Back when I first bought my fuels I always rode them 4 line mode but they give you so much better upwind with a slightly slack 5th line that I gave up riding them 4 line and always ride them 5 line mode now.
The Vegas 5th line tension has to be perfect. For the Vegas unlike the fuel you don't want this 3.5 inches (90mm) of slack you want it to be perfectly tensioned. If you fly the kite you should notice that both center lines and the 5th line all look equally tensioned. I would have to look at the North Trust bar, I can't remember off hand if it has an adjustment somewhere to get that 5th line tension correct or not. Anyway fly the kite look at the lines and you can easily see if it's correctly tensioned. North sets up their control bars and lines so that when new it is perfectly tensioned for all kites. When the lines get older though and shrink/stretch that's the only time you might need to adjust the 5th line.