Kind of a strange request... so many factors to consider beyond simply looking for a silver bullet to over ride the speed limiter... tires, shocks, brakes, ride height, drag, and, oh yeah, the nut behind the wheel... things happen quick when it goes to sh#$# at a 100 mph... can imagine an average driver keeping up with all the bad things that could happen at 170... fact is, unless you tweaked your over the counter IS 350 with all of the things that make cars behave nicely when you venture on beyound the buck 50 mark I doubt that you would want to drive one that fast... and, now that I think of it, I can't think of any racing venues in this country where your stock IS 350 would see 170 short of Daytona or Talladega and then you would have to factor in that same old question, will the car be up for the run.
You would be better to invest your time an money in tweaking this fine car's handling and driving characteristics... think tires... than messing with the engine management system in an effort to make a Banzi/suicide run in the car... believe me... there is a skill factor involved in peddling a car into those mega digit speeds.... and yes, I've been there, done that...