I'm not sure having the two guns (even moved down to level 7) is enough of a balance of moving so fast.
For every benefit, there needs to be an equal drawback.
It seems like the arrow would need to be very, very weak if it's going to be so hard to hit. I mean, if it couldn't mount a shield, or maybe if it could only have a very low level shield it would be more balanced. I think it's just going to be way too annoying of a ship to kill, since it can dodge almost anything and can't do any real damage. Maybe make it so it has no counter-measure dropper? That would be a serious drawback!
It would work well for factions, but without more balance smugglers are going to have yet another exploit-- plus when travelling faster than 350 it's going to be really hard to tell if someone is using the speed mod unless you are close enough to see that they are in an arrow. This will lead to more false accusations of cheating and even more work for the admins, don't you think?