I have a TM VSR and I love it. IMO the G-Spec is the only version thats actually made for a sniper, its bolt on rotated 45 degrees where as the other two rotate 90, it also has a very effective suppressor.
Really the only things you need to upgrade in it are the piston/trigger sears, the actual piston, and the spring... Maybe a barrel, however I just polished mine and it shoots just as well as any TB barrel I have seen.
sticks