Look in the machines specs on the Haas website for the motor torque; I think maximum is something like 175 lb ft at a few hundred rpm...could be faulty memory though.
You are correct about torque being an issue with a direct drive/no gear box. I have machined 8" OD aluminum and 4" leaded steel and it is easy to run the spindle over 100% even with modest depth of cut (0.06") and feed (0.005"/rev).
The TL2 has a bigger motor than the TL1; 12 versus 7.5hp but it can only do longer parts not larger in diameter. I don't see the rigidity being much different, the only difference is the main casting is a bit longer but it is the same cross section.
I think you might be pushing it on 6 - 8" stainless.