cold setting 3-speed road frame to 7 8 speed cassette So my old road bike has a 3-speed freewheel, dropout spacing is about 114 mm. I'd like to give it an upgrade and put a 7 or 8 speed cassette (maybe stick with a freewheel if 6-7 speed, I just want more range and less hustle) 

Spacing of a modern cassette-type road hub is 130 mm. As the Sheldon Brown bible says cold setting is achievable but it doesn't say how many speeds you can go up. Many people go from 5 speed to 7 speed, or from 7 speed to 10 speed, but I couldn't find anyone on the internet who tries to go from 3 speed to 7 speed. My worry is that it is too much difference I have to spread apart and that it may damage the frame. My weight is on the heavy side and I don't want to end up with my teeth on the road :-P

To sum up, will it be safe to resize from 114 mm to 130?
Cold setting a 114mm to 130mm is significant. Usually the rule of thumb for cold setting is you can go up one step, such as from a 126mm to 130mm or 120mm to 126mm. A three speed freewheel bicycle is extremely rare and I'd personally leave it alone, it's just too valuable to risk destroying the frame.