I have driven the IS 350 twice, and I have a G 35 (similar motor with similar characteristics to the IS 350). I also have a 335 i. IMO, an IS 350 is not in the same league as the 335 i (performance wise), or I would have purchased it instead of the 335 i.
There's no telling how someone got a single 0-60 time--amazing launch, wind, downhill, they're lying, ..... The car isn't as quick, as fast, doesn't handle as well as a 335 i. Nice car, though, and it has ventilated seats--a great option.