http://www.mycpu.com.hk/1674/
(Traditional Chinese)
Four full samples at high ISOs are posted but only one is contained with full EXIF. Moreover, the silent mirror/shutter mode and the standard/normal mirror mode are compared in the following videos:-
(Above: Normal mode)
(Below: "Silent" Mode)
It is easily noticed that the mirror action in the silent mode is not as loud but it also looks slower. In fact, to make both a fast moving and slient mirror is really technically challenging, which I think only the EOS 1 series bodies of Canon will give you that (but not a 5D).
Btw, the same limitation can be found in the K-5, the K-5's mirror action is silent and gentle but I don't think its response could really be considered quick and fast - I feel that it is somehow a bit slower than my original 5D.