Here's how much deflection we get with no additional strips and only two sides on (no back). This is already acceptable considering that I'm not as wide as the telly and I'm sitting in the middle rather than spreading the load the whole width of the shelf; the telly's 22kg lighter also, so there would be pretty much no sag at all. Nonetheless I'm still gonna add some 2cm thick strips below this shelf for extra stability when the cats jump on top of it.