I read about Mystic CCs (= LC 575) pushed to the limit with use of a 128 MB memory module. I verified the nice operation of such module in a LC 475, no issues besides the extraordinary long duration for the memory count step in the boot process. In case you want to purchase a 128 MB PS/2 RAM module, be aware of the fact that not only different elctrical specified modules are available, but also different physical dimensions. Some modules will not fit into most machines without changing the angle of the slot or cutting out in the case. A module specified for a Performa 630 might be electrical compatible to a LC 475, but might interfere with the CPU chip or a heatsink.