Couldn't find any reference to it in any of the 4th or 5th edition stuff I have. Probably something that will be statted out in the 5th ed version of Arsenal, which doesn't help you now. Meanwhile, you could look at the Yamaha Raiden, compare how much better it is than other assault rifles and extrapolate from there. For example, the Raiden has a 6 ( 8 ) accuracy. So look at the machine pistols, see the best is a 5(7) on the Crusader. So give your Seiten a 6 ( 8 ) accuracy. And so on. Just let the players know those stats can/will change when official stats come out.
Edit: Had to get rid of the damn smilies.