IS3 is made of paper compared to the IS4. Stick with it, it really does pay off. I never lose money with the S-70 mounted and the IS7 has taken no time at all to unlock. I won't be using the IS7 though simply because I went from the VK4502 to the Maus and the fights become way harder. Its much better to sit at tier IX with a tier X gun and stomp the field. Unless you play clan wars of course, then the tier X is a must.
