Im not expert but you're probably good with a size 6.5-7 on Pradas and Guccis. Really depends on how you want it to fit whether snug or quite loose. Also depends on the shape of the shoe and your comfortability with it.
Anyway im not sure if i can provide updates in here but its related to high end designer shoe anyway.
Just came from LV flagship store along Canton Road in Hongkong.
Punchy in both green and red canvass is still at a full size run as of 05/31/10
LV Dons in all colorway produced (Red, creme, grey on white, patchwork, black suede) biggest size available was 7 (lv sizing)
LV jaspers in white 6.5 was the biggest available, Jasper
Some other sneakers in the 2010 catalogue is still pretty much available in common sizes.