I must admit 0.7x magnification at minimum focusing distance of 7.87 does seem awfully handy, especially since a small macro extension tube (with electrical contacts preferably) will easily make it a true Macro lens.
No, actually - it won't. Add a 12mm tube, and the max mag goes down. Add a 25mm tube and it goes up to a 0.72x (at the wide end, it's 0.4x at the long end with the 25mm tube).
Huh, can you point me to the calculator or formula you are using?
I'm getting 0.94x magnification with 20mm extension tube added to the 70mm telephoto end using the stated minimum focus distance of 20 cm. I'm using this calculator: