Originally Posted by TejanoTrackie

I again disagree. Let's deal with hard facts here. I happen to have frames with 120mm, 126mm, 130mm, 135mm and 140mm rear dropout spacing. I also have unmodified wheels that fit in these frames. I know for a fact that there is no difference in the distance from the left (non-pulling) flange to the dropout face on my 120mm and 130mm wheels (~30mm), but that there is approximately a 10mm difference between the distance from the right flange to the dropout face (~37mm vs ~47mm). So what this tells me that if I wanted to stuff my 130mm rear wheel into my 120mm frame without further dishing the wheel I would have to spread the right chain/seat stays 10mm at the dropout. When I visually compare the frames, it is apparent that the left side stays are angled out about the same, however, the right side on the 130mm frame is significantly more. Mind you, these are both road frames and road wheels, and MTB frames are a
little different, however, the OP's question relates to spreading a road frame from 120mm to 130mm.

As far as your assertion that frames are routinely cold set, I'd say that this applies only to steel frames and only 2 or 3mm at most. Furthermore, properly made frames are heat set in the jig to minimize spring back when they are removed. This is more of a problem with TIG (hot) welding than low temperature brazed lugged construction, which is why all of my old steel frames are lugged. I will maintain my opinion that spreading a frame 10mm is not a good idea, however, you and the OP are welcome to yours as it none of my business what you choose to do with your property.