It's an extreme stretch, but it is actually possible to get Light Speed Jonathan. Before drinking Joseph's blood, Dio couldn't use his vampire powers; so any physical feats he displays are things Jonathan could do without using Hamon. In that state he has no trouble blitzing Joseph, who dodged a beam of light from the Red Stone of Aja during his fight with Kars. Any speed Joseph lost from age is more than outweighed by the speed Jonathan's body would be losing from not being to use Hamon; therefore Jonathan has Light Speed reaction times. Of course, this is built on highly questionable logic and a great deal of assumptions; but as researcher's blog said to use Parts 1-3 as resources for determining how strong Jonathan is we may very well see him being scaled to Joseph and Part 3 Dio.