Have a look at the above test. The test is clearly described and the results are self-explanatory. See:-
So, it can be quite safely concluded from the above that the mirror slap is an issue for the K-5 and it causes obvious blur in the final images, especially when a longer focal length is used. And, against what Pentax camera operation manuals always advise for turning off the SR when mounting the camera on a tripod, turning on the SR could reduce the effect somehow, but however the problem and the adverse effect is still not totally eliminated, unless the mirror is locked up.
Do note that it is the mirror slap that causes blur but not the shutter vibration, otherwise even locking up the mirror cannot help.
All in all, the K-5 has a higher pixel count for an APS-C DSLR, but without a more accurate focusing system and a more gentle mirror slap that cause less vibration, most of the effective resolution of the sensor is actually wasted and the image quality suffers. And, if the higher fps is the cause of all those mirror slap problems for the latest Pentax DSLRs (i.e., K-7, K-x, K-5 and K-r), I would rather have a 3 fps rate in the old days for all those Pentax digital bodies! >:-[