I agree with the keeing the car stock. I remember the Griffith license test in GT3 on SS11. What a pig that was, but I kept at it and golded it. Amazing the improvement I managed with practise.
You should be careful comparing TVR models. I have a Tamora (similar to the T350), which is really great to drive, the Tuscan is much harder, more floaty suspension and more understeer. The Griffith is a monster.
The Griff has a big V8 with lots of low down torque. The Tam/T350 & Tuscan have the Speed6 with progressive torque. My car scares me when the rev counter goes past 5K, it seems to suddenly get even more acceleration.
Steven