I laced a wheel-set or two 6x some time ago and it's definitely more rigid. The wheels were 48h and were used for street. During which time I rarely bothered truing my wheels and now that I think of it comparing, 6x held truer over time. But hey, that was some time ago when I did such thing because the spokes I had were too long for 4x. Let us know how the lacing turns out on a 36h for you.