there are lots of other factors to consider.
what alloy is the steel? wall thickness? radius of bend? weld technique?
Some steels are very forgiving of heat, but many high strength tubing alloys will change radically when heated, depending on how they cool, as well. Some steels, with higher carbon contents, may want to be annealed after heating, then re-heat treated, to achieve specified strength.
If you are using plumbing pipe for your frame, sure, go right ahead and do it all hot.
The angle of the bend is one thing, but the radius of the bend is a totally different thing- long gentle bends are much easier to do and much less likely to cause cracks or stress than tight radius bends of the same angle.
I had a good friend who was a real guru- and he did a lot of bending at black heat. Just heating steel up to 500 to 800 degrees makes it bend much much easier, but is less likely to radically change the material.
Commercial motorcycles are engineered to be made from the lightest possible material for the application- but that means precise bending, welding, and heat treating, depending on the bike. If you over-engineer to account for homebrew techniques, your frame may not be quite as elegant as one that has been stress tested to destruction a few dozen times.