OK....
The SPEC C is a superior "drivers" car imo, but is very raw compared to the A45. I haven't taken the A45 on track yet (will do though), but the SPEC C was pretty epic in that discipline. As a comparison, I took part in a race event called Tuner GP back in 2005/6. The SPEC C was at around 370bhp and I came 4th in class, beating quite a few big hitters, with one being a 500+ EVO race prepped tuners car. SPEC C's are quick on track.
Personally I love the A45. It's quick, comfortable (relatively) and is quite special imo. The A45 (price aside) is exactly what the STI should have evolved into. I don't regret the change one bit.
As you mention the RS, I would suggest you wait to see how that goes. I think that car will upset the mid range models across the board. At the price it has the potential to be quite a car..... and you know that tuners will be jumping on the back of it!
I'm an old Cossie boy.... so I'm really hoping this RS does the business.