A warp bubble does not impart any additional force, the bubble bends space so you are not technically moving at all, instead space is.
Basic physics says it would takes the entire power of the universe (infinite energy) to reach light speed, so there is no way the warp core does that. If it did any warp factor above 1 would have to destroy the universe if it imparted that energy to the target - so it can't work like that. Its been stated that the bubble moves space not the ship, so a ship at warp would be no different than one at max impulse (its not moving any faster than it was)
There is no way to reconcile the problem if at warp you release enough power to destroy the entire universe (and multiple times over above warp 1), so it can't be transferring momentum into energy
The same effect would have to be present for a warp core breach too, if that's how it worked but it isn't, one warp core goes bang so does the universe (as it would need to produce enough energy to cross the light barrier, which we know it doesn't), so it cannot work that way. Therefore the only conclusion is that ramming a ship is no different than a torpedo (its the detonation not the impact at warp that does the damage), ramming at impulse makes sense though as you get the impact and detonation
Bottom line is that warp does not (can not) travel faster than light from a momentum point of view