At lower lv I think taking flash as a cross class skill is not a bad idea, since you still need to get used to your TP usage and berserk pacification timing.

As for skill speed vs TP drain, I don't think at current content you can reach high enough skill speed that you'd be drained of TP, unless you can't use equilibrium every ~60 sec to recover TP. Pretty sure someone did the math a while ago, and warriors with access to equilibrium has positive TP change rate while doing single target rotation, so they'd never run out of TP. Of course this is only for single target rotation, but my point is, you don't have to worry about having high skill speed.