I got a 1.01 as my fastest, not great I know. Only spent half an hour doing it just to get the car.
I think if you can be bothered, and have the skill to put in a good time then drive for a few hours, allow the engine to break-in and gain more horse power and then put in the fastest lap. Just an idea.
A way to counter the under steer - if you're any good with the car then slide the nose of the care into the corner under braking so that when you accelerate the car is pointing in the general direction of the exit. That way the car requires less steering and therefore lessening the problem of under steer.
I think if I spent a day at it I may get under 1 minute but I just can't be bothered to be honest. My driving skill are OK, I'm a fairly good racer but I hate time trails.