I use both spacers and also general placement by aligning the spline points so that they touch the edge of the ties on both tracks. That seems to match the 5m track spacing pretty well.
Up here in the Boston area, our track spacing varies considerably. The oldest lines, such as those on the north side are as close as 3.5 to 4 meters. Those lines that were built later are 4 to 4.5 meters with some up to 5 meters. We also have lower bridges and tunnels making double-stacks impossible on the Hoosac Tunnel route.