I think humans have been partially doing this. I mean, think of all the species of plants and animals that humans have made extinct, directly or indirectly.
I have a feeling this thread will have arguments about whether certain mods are cheating or not. Hopefully, it won't happen.
And yes, I use MechJeb. IMO doesn't make me a cheater though...
I've never used them before so I don't really know but I think they are more efficient than other engines aside from the fact that they only use liquid fuel. Probably great for interplanetary transfers...
EDIT: ninja'd lol