A 5/8 is still not the best for a mobile installation. Let's look into that a little bit.
Just like statistics and our government reports, they can lie. Notice that the well circulated 5/8 vs 1/4 modeling represents perfect ground. A vehicle is not a perfect ground extending out tens+ wavelengths. For explanation purposes I'll use the amateur 2m band. Perhaps if one places a 2 meter 5/8 wave antenna on a lake freighter we would see a 5/8 wave advantage bow to stern. Model the 5/8 wave over a ground plane typical of the average sedan one would see the 1/4 wave clearly outperform the high angle radiation of a 5/8 radiator over the minuscule and imperfect ground. Side to side, a typical car's ground image is barely over a 1/4 wavelength; which is very far from perfect ground. Ground loss will affect the pattern, especially the gain at low angles such as the 5/8 antenna.
If one needs more gain on the horizontal plane, look at purchasing a collinear stack. Bottom line is that the 5/8 wavelength antennas are not the best performers in a mobile instillation and 1/4 wins in a typical mobile instillation with typical varying conditions as a mobile would experience. The theoretical difference is about 1.2 dB, but in the real world where terrain always varies and will be hilly or even mountainous, the 1/4-wave is the better performer. I know I'll get the anecdotal evidence crowd to defend their installation, and the ones who have been designing antennas professionally for 120 years with antenna theory and EZNEC modeling, but the 5/8 is really for base installs that can actually take full advantage of being a 5/8.
As for me, I use 1/4 wave on all vehicles mainly because I live in hilly terrain and they just work better. Not to mention I can pull into my garage without hitting anything.