Ok guy , i asked here and you can assume that the locks causes synchronisation between GPU and CPU ...that's to say that your CPU can wait a certain amount of time waiting that driver doesn't need the resources anymore especially when having some frames of delay in the command buffer (eg presentation intervall other than immediate).
we have had this problem on a big game like Crysis here, and the lock time was driver dependent...

Try to deactivate lock if you can and capture and you will see if it's the pbm...

Looking at your PIX scrns you have 16x to 50x more texture locks then the crysis traces show, if these are texture read backs avoid them as they are really intensive especially if you after reading back upload them to the GPU again.

Also try and avoid using the User Primitives as they might upload their data to the GPU on the fly wereas VB's are uploaded as soon as you unlock them. The UP calls need to upload the data and don't return untill they are done doing this, look at the documentation of these functions.