The guide number gives the (nominal) number of meters away a subject can be to be lit at that focal length and ISO, at f/1. Divide by aperture to get effective distance stopped down to the realm of real lenses — that is, the Metz 48 AF-1 is listed as providing full lighting at about 3.6 meters away at f/8. (That's approximately 12 feet, for those of us accustomed to the Imperial system.)
This really ought to be tested by someone with access to all of the flash units and a flash meter to give a perfect answer, but this is what I can do with the publicly-stated data. With some scouring of manuals and official web sites, I put together the following list of manufacturer-claimed guide numbers (in meters) for ISO 100 at various 35mm-equivalent focal lengths. I don't have any particular reason to distrust the numbers from Pentax, Metz, Sigma, or Promaster, but as detailed elsewhere on the site the single number given by Sakar doesn't appear to be honest.
Remember to divide by 1.5 to get real focal lengths for Pentax's current APS-C dSLR bodies. The list is ordered by guide number at 50mm, with the Sakar unit placed at its estimated position.
✗ indicates that this flash does not have this zoom step.
1 With built-in or included wide-angle diffuser.
2 Names include Tumax DSL283AF, DSL286AF, and DSL288AF; and Vivitar DF-183. The Metz 24 AF-1 is also related, but is listed with a slightly higher guide number.
3 And other variants, like the Metz 36 AF-5.
4 There are many variants of this flash on the market, some with slightly differing stated guide numbers. See table of OEM labels.
5 Both Super and ST models.
6 The 58 AF-2's wide-angle panel is more diffuse than that of the 58 AF-1, covering 12mm instead of 18mm (a whole 23° wider).