As I said in my original post, there does not appear to be any frame damage other than the dent. If you look at the attached photo it is on the underside of the down tube just in front of the shifters.

The Bike exchange has a fairly well equipped shop but there are no "frame tube straightening" tools and none are needed except to work out the dent.

Again I ask "is the down tube in compression or tension?" If it is in tension I would think a dent would be of little significance.

So, does anyone have the expertise to answer my original question?

If I can get most of the dent out this way will the frame be sufficiently strong?