I spent the evening designing the filmholder for my homebrew LF camera and 4x5 negatives look so small right now...
Should I adjust my camera design to accomodate 8x10 already?

Problem is that 4x5 negatives are still easy to find here in Belgium but I've never seen a shop that sells the bigger stuff.
I've read that 5x7 is also difficult to get. Is it easy to buy online?

And now the technical question: I bought a box of Polaroid 559 "silk" that was over date (a real bargain) to fit it in the holder. The thickness of the negatives feels less thick than regular MF or 135 film. Is this correct of does the size of the negatives give it a more flexible feel?