Color rendering/rendition index doesn't mean much for plants. You could 'knock out' the sun's entire spectrum from 500-600nm and grow plants just as well(making CRI drop significantly). Case in point: HPS, very low CRI(around 22), flowers plants very nicely. Gro Lux(one of the best, based on the spectrum of light produced, Phillips PL/AQ bulbs don't have as much red, nor is it in the ideal location 660-700nm like a Gro Lux) and other plant specialty bulbs also have a lower CRI(89 or so compared with some fluoros that are in the high 90's) than the best CRI fluorescents. Also many halogens have 100 CRI, not the best for plants, though(lower efficiency).
Then again MH CRI ranges from 70's to 90's, all of which grow plants nicely, but the lower CRI bulbs probably do it better, as they have more intense spikes in the right locations, meaning more watts of radiance will be utilized for photosynthesis, and less watts for radiance which will not promote photosynthesis. The most important measurement is the only measurement that matters, the photosynthetic photon flux, micromols, microeinsteins, however you want to label the term used to measure the actual radiance in the correct wavelengths which support photosynthesis.