Understood. The thing that surprised me, was that reducing the length of the span by just 200mm means the 63cls gives less deflection than the 89cls at 1900mm. But I suppose it makes sense given the equation: (5wL^4)/(384EI). That power of 4 means even slight reduction makes it significantly stronger. On a normal bed this wouldn't look too good with the legs stuck closer to the middle, but for my trundle bed not much of a problem.
