The effect of mirror on image quality is, according to somebody, visible for shutter speeds from around 1/4" to 1/30" or so.
From 1/125" the effect should be small. There should always is a loss of quality, so you'd better raise the mirror if you work on tripod, but whereas at 1/8" raising the mirror gives a clear gain in image quality, at 1/500" it doesn't, using a normal lens.
That said: when using a tripod and if you have mirror lock-up, do use it always.
If using the camera hand-held, the real difference can be felt at 1/15" or 1/30" which are the two speeds that one may be induced to use free-hand and which exhibit more the effect of mirror slapping. If you normally take pictures in normal daylight conditions, and your shutter speed normally is above 1/60", I wouldn't worry about the effect of the mirror on quality, it's hand-holding which, in itself, degrades quality more than mirror.
I've read conflicting reports over sharpness at high shutter speeds with or without mirror.
My impression is that tripod work is always superior, at every speed, to hand-holding, which leads me to believe that also at 1/500" there is a decay caused by the hand shake.