I compared the two cars when I was buying the 335i and I have to agree with a number of people here about how IS350 handles. The car does give you a rush when you hit the gas off the line, it does have lots of power and seems to get it to the wheel.
The most noticeable different between the 335 and 350 is the fact when the turbo kick in it throws you back into the seat, where as the 350 is more of a constant acceleration, it does not have the throw back feeling. The 335i is like driving a 440 roadrunner with the electric hood scoop, you hit the button on the dash, the scoop pops up and you are thrown back in to the seat as you accelerate down the road.
The other issue with the IS350, is the fact it has all the power and a spongy handling. That alone will scare the hell out of you. When driving the car I always felt I had no idea if the car was on the edge of its performance. It felt like it was about to break free.
The best part was the sales guy trying to tell me how well you can feel the road through the car and how much better it was then other Lexus. I never drove other Lexus so I would not have any idea.
I almost bought the IS350, since I drove it after driving a 330i, prior to the 335i coming out. I am glad I waited and drove the 335i.