I did not notice any difference with my front STB (cheap Taiwan style) on or off. In fact, I took it out as I find it more of a benefit to have easy access to the oil cap. I believe top STBs don't do a whole lot on a stock suspension car. There is enough slop in the suspension bushings to take up any movement before chassis stiffness even comes into play.
This is a bit of a religious argument, however, and a lot of people believe they feel a change after they install a particular part because they spent money on it. Sort of a psyhosomatic thing - you feel it cause your brain thinks it should. Only way to know for sure if people can tell there was a change is by using one of these two techniques:
- have a professional driver run several laps on a track without the mod, then install it and observe for any changes in lap times.
- do a double blind experiment, where someone installs the bar without you knowing about it and see if you notice anything afterwards.
I do have the ES shock tower bushings installed now, which are much stiffer than stock, so I might actually notice an improvement. But I'm gonna wait till I can get a really stiff STB like RREs tubular steel ones. Those flimsy tubular aluminum kinds are more for looks than function, IMO.