The tC is by no means a "fast car". Most mid size sedans now a days have anywhere from 160 to 250hp at the wheels, so don't expect to win at every green. On the other hand, the tC is by no means a slouch. 160hp with a 5 speed will get you from a to b and put a smile on your face

Sure the tC will probably only give you mid 7's 0-60, but if that's not fast enough,
get a supercharger! And you're right, going from a v8 to the tC is taking it down a noch. The tC would be a lot faster if the damn thing didn't weigh 2900lbs (i still have no idea how a 3dr hatchback weighs that much...). I on the other hand will be going from a mutty 108hp 3speed (yes, 3speed no overdrive) auto 95 prizm to the tC soon. So even if i just stick with the factory engine it'll feel 1000x zippier
But anyway, I think you should have a friend sit in the car with you (find someone that wont weigh your car down too much, lol) and clock some tests. maybe a 1/4 mile and a few 0-60's. Just a thought.