Brian - the Readyload and Quickload holders were the worst - bent the film badly near the
insertion side. I heavily modified a 545 holder, but it will only get about two more trips out
of it due to my film sleeves running low. For color 8x10 I use adhesive holders, since I'm
more likely to make a big color enlargement than black-and-white, which I print only up to
20x24. Most black and white film is stiffer than color anyway, though the Kodak estar base
is pretty good. For ordinary 4x5 work I just use regular Lisco or Fidelity holders - the smaller size buckles less than 8x10. But I check my camera film plane with a special depth
micrometer. Once found a few air bubbles in the varnish that might affect focus, and sanded these out. Never had a warped back or holder yet, but then, I've never bought used holders.