Sharpness is not everything in a lens. You aren't blowing it up to poster size or selling a %100 crop to a national glossy magazine or something. The FA wide open is plenty sharp for most people's needs.
Now, hurleygirlie it seems you are rather new so please forgive me if you already know what I'm about to tell you. And I'll also recommend going to
Pentax Beginner's Corner Q&A - PentaxForums.com as it's a great place to learn. All of this is my summation, which is roughly accurate but I make no claims at expertise.
Now, think of each picture (exposure) you take as having a triangle of factors: aperture (f-stop number), iso, and shutter speed. Aperture is the size of the hole that lets light onto the sensor (smaller the number, the bigger the openning), iso is how sensitive the sensor is to light (higher the number, the less light is needed to make a proper exposure), and shutter speed is obviously how long light is allowed to hit the shutter. Each of these also affects something else in the exposure, and that's what you want to concentrate on.
Aperture controls depth of field (DoF), which is what range of distance things are in focus. The larger the aperture, the shallower the DoF. So for example, let's say you're taking a picture of a dog with a long snout, facing you head on. A very small aperture (higher f stop number) might have everything from the tip of it's nose to the end of it's tail in focus. A very large aperture (lower f stop number) might only have the tip of it's nose in focus.
With iso the main concern is "noise" the little specks of random colors or grains that appear at the higher iso numbers. This greatly varies between bodies, with the K5 having the least noise at the highest iso numbers.
With shutter speed, it depends on subject matter. If the subject is not moving and the camera is on a tripod, very slow speeds can work well. But for hand held shots of moving subjects (such as candids of children) you probably want a higher shutter speed to "freeze" the action, so to speak. Of course if you use a slower shutter speed the subject will be motion blurred which can be a very artistic effect, but generally you'll want a higher speed.
So, a lot depends on the body you are using, and the lighting conditions etc. I find that indoors the advantage of a zoom (not having to move to have a closer shot) are far less than the advantages of better image quality and larger aperture afforded by the primes such as the FA 50 or DA 35 f2.4AL. Especially with the K5, I tend to use TAv (I set the aperture for the DoF I want and the shutter speed to something I can shoot by hand without blurring, then the camera sets iso so the exposure is correct) and the results have been excellent. Also remember that, especially with the higher resolution of modeern bodies and the excellent sharpness of a good prime, severely cropping a picture to correct the framing etc is a great option.