I don't envisage doing anything larger than 20x16, but it did cross my mind that when I printed 6x12 larger trays would be useful. With 24x20 trays I could print 20x10 with a border, I did wonder if this would be large enough for exhibition, if I wanted large panoramas, so I got 3 trays which were approx 1.2m by 0.9m, which sounds the same size as the Silverprint ones you mention. Only problem is they are so big, I can barely fit them in the darkroom hence they are totally impractical in my darkroom (I didn't really think through how big an area they take up side by side) so it looks like I will have to stick to 24x20.
I have still got the large trays, as I was thinking that I could just about use them in my darkroom if I wanted, but the more I think about it the more I think it would be disastrous, I barely have room to move between the benches! and I can foresee chemical spills on a large scale
Neil