[quote=@Forsythe]
Ok, let me say no to normal space FTL straight away. That is a potential relativistic weapon right there, and I'm having none of that, not even speeds like in stargate where ships clocked at 0.6c. If somebody wants to render a planet uninhabitable, they're going to have to put effort and risk into it, not just send a comet at light speed at anyone they don't like.

As I said, the relic to start with is not necessary and you can ask for something else or nothing at all, my folks are at disadvantage by design too. I just don't recommend continuing down that road with the relics you discover afterwards, that's a shortcut to getting extinct xP
[/quote]Just because something travels at FTL speeds in "normal space" doesn't mean it would have the same energy (hell, given relativity that's an oxymoron).
Warp drives either warp space or manipulate mass to mess with relativity. Either way they can't be used to make RKKVs because they essentially cheat exactly that. In case of the former the ship is actually well below the speed of light but warping space acts like a multiplier. In case of the latter your ship has no mass to speak of so it cannot impact with any force. Either way once the FTL effect is off the ship would return to the level of speed its normal parameters would demand.
I don't like the Mass Effet interpretation (and it'd also lead to abuses in other ways) so I would stick with the classic space warping effect. That's roughly the same method you can use other FTL methods to. Just without accessing another dimension.

On the other hand like it or not RKKVs are damn easy in any such setting. Just attach a cheap engine on the asteroid and wait till it gradually speeds up. Though I don't say they are truly effective means of warfare here. Intercepting them would be child's play.

Also I hope you have nothing against FTL sensors because they are very essential for any interstellar NRP. Not as much as FTL comms but close. This is something not all people realize.