I used an o-scope setting all of my gains..
On my system it didn't seem to matter what frequency I used I tested about 10 from 30hz to 20k.. At every point in the system the signal clipped at the same point..
For me. the HU started clipping at 28 of 35... then the WS420 controller was fine wide open if all of the frequency EQ were at 0. Then bumped the amp gains up till they started to clip and backed off. I didn't notice the point at which anything clipped to be dependent on frequency.
To your question though.. I think you would be fine at 100hz.. I dropped mine REV410s to 80hz and haven't noticed any issue. I wish they had more midbass punch though