45kg, that's a lot for sliders and should be enough. I have seen images of other heavy duty rails that were a lot more massive (twice as high). That's the reason I wanted to use wheels instead.
I'll see if I split the high slider cabinet into two sliders. The upper slider will be a lot higher than the lower slider but heavy stuff is usually stored lower anyway so it should stay realistic. I does solve the problem I'm having with the center border so it's a very appealing solution.