I have a Bacchetta Agio. It's aluminum. I usually prefer steel, and I don't care too much about excess weight. However, mine is a LWB, so it's not too stiff.
The Giro, being a SWB, will be stiffer. Take both aluminum and steel for a ride, and see what you think.
Also, I have discs on my Agio... discs are overrated. Can you get your LBS to build a steel Giro with better components?