Arent the S-Techs close to a 2" drop or so? For the tC it looks like (From what Raamaudio/Rick has done as well as some other sources) that 1.4 inches is about the max you want to go. As you lower excessively, you run into the issue of needing overly high rates, like is happening here as well as the roll couple actually getting larger at some point, so you really arent battling roll any longer, but actually making it worse to some degree. I would go with a milder drop for sure.
My setup seems to be decent so far. I wouldnt mind having the hotchkis sway bars in place of the TRD, but for a mix of autox and daily driving it is doing well for me the way it is. I am at the point that the driver has more room to improve (which is normally the case) than the suspension does I think
I will run it another season, then see if I want to further tweak it. This years changes will be tires and some alignment work. A little negative camber up front will help it bite more there and rotate for you.
I am hearing from some guys in our autosports club here that the tC is doing pretty well in its stock class. I cant say, since I have only seen another tC at our events once. Some guys in our club that run in multiple states as well as nationals have seen more of them out there so they have seen more of what they can do.
In STS, it can hold its own if you set it up and drive it right, but the older honda hatches and integras will make things hard for you (and everyone really!) there. I was running around mid pack out of 20 - 25 cars in STS at most of our events last year on all season tires. With that season in the tC under my belt, some stickier tires and some alignment work, I am hoping to be closer to the top 5 this season. In our club, that is very respectable in STS so that would definitely make me happy. STS is very competitive for us here, especially with some nationals level guys and cars in it.
Power wise it does fine in STS. The low end power is handy to have for sure, and most other cars out there in STS are not power mongers either. It is a second gear car all the way. I never shift during a run. There was a very tight pin turn at one event that was slow enough for first gear. But the tough shift to first in the tC and the shortness of the gear wasted more time than just leaving it in 2nd, doing a quick clutch to get the revs up afterward and letting it run.
I am still working to get faster through the slaloms. I enter most standard spaced slaloms at a little over 40mph, but it depends on the lot conditions for sure. It can get a bit touchy with you if you upset it by changing speeds (slaloms should be done at a constant speed) or getting off a smooth line too much. I get some pretty serious rotation every now and then if I get out of time on a slalom, and have had it come all the way around before as well.
Boosted, you will be running with a wide variety of cars as well, so you will have some fun competition for sure there
But, I have seen some pretty unexpected cars do very well too. The driver is very much the deciding factor.