A prime likely still has several advantages over a zoom at a given focal length. (Well, depending upon your needs and habits.)

• A less complex optical design. All else being equal, a less complex design is likely to have fewer compromises, which means the prime is more likely to have less distortion of any sort -- pincushion, barrel, coma, and chromatic abberations. And on the flip side, a sharper lens.

• Maximum aperture: an f1.4 prime is two stops faster than a "pro" f2.8 lens. 3 stops faster than a consumer-aimed f4. That lets you use a shallower depth of field and see in dim light much more easily.

• Focus speed: a less complex design almost definitely means less weight to move to bring the lens in focus and a larger aperture lets in more light to make focus more sure-footed, so the focus speed can be faster.

• I wasn't sure what you meant by "speed." Focus speed or aperture speed? I covered those. Here's one more: composition speed. With a prime I don't need to twist the zoom ring to get to 50mm -- I'm always there!

• When comparing to a consumer lens, the prime also typically has a focus scale and a much smoother focus ring (with a longer throw, too).