Why ? xd ...Why are you trying to run a video card so out of recommended specifications. Why are you asking about theoretical o/c situations when you don't have the correct psu for even normal operation ?
Lol. I undervolted my CPU which gives me the extra power I need to do minor overclocking. Also earlier laptops in the same series used the 65nm core card and had the same PSU. I am also planning on buying a 150W or 180W PSU eventually to replace mine when I upgrade to the Core 2 Duo T9900 which uses 10 more W, so I don't care if I'm pushing my current PSU. I also feel that laptop graphics cards can be overclocked more than desktop ones if you have the proper cooling, because with laptops, they have to assume that you don't.