Regarding the StarViper and formation flying, couldn't you just give Xizor a wingman or 2 of other StarVipers? They all share the same dial and maneuverability, so the others should be able to keep up with Xizor.
The other thing people are ignoring is that Xizor's ability makes him very likely to be your endgame piece. So even if he starts out flying in formation, there will come a break point where the leash comes off and he starts pulling crazy maneuvers.
I still can't say if he'll be really effective, but his options aren't as binary as "fly in formation the whole game" and "don't ever fly in formation".
Another thing I thought to do along those line is give him Lonewolf as an EPT, start in formation where your buddies soak some hit IF your opponent decide to target him and then, once the field is cleared and you get in the end game, start flying on your own and benefit from lone wolf.
Here's a sqaud idea I have that fit both idea: Pure Chaos or formation until the end-game:
Xizor + Virago + Autothruster + Advanced Sensor + Inertial Dampeners + EPT (Push the Limit or Predator or Lonewolf)
Syndicate Thug + Ion Cannon Turret
Binayre Pirate
Binayre Pirate
Binayre Pirate