Re: Ramming planets at warp velocity!
Warp drives take energy to operate. So whatever energy is used to generate the subspace field would be dissipated into the environment by the conversation of energy. The total destructive energy has an upper bound of whatever store of antimatter is aboard (ignoring chemical explosives and nuclear fusion or fission devices such as the impulse engines). The lower bound is a kiloton to gigaton nuclear explosion (the impulse engines exploding, from The Doomsday Machine). They probably have enough destructive energy to blow away the entire atmosphere (as per Obsession).
"Is this all that I am? Is there nothing more?" - V'GER
"Don't tell me what it can't do: I built the damn thing!" - Emory Erickson