I have thought that a light weight road bike would serve me better on my daily rides (I have an old aluminum Raleigh hybrid....but average only 14-16 mph on my 40-55 mile rides and see many people with true road bikes going quite a bit faster and thought I would need a better bike to get involved with group rides and week long tours.
I'm skeptical about the value of a "go-fast" bike. The weight of a bike doesn't make much difference to your top speed, though it does make accelerating a bit harder. I regularly ride with a group that rolls along at 20-25 mph, and I lose them on the hills (I suck at hills!), then catch them on the downhills (gravity likes me!) and proceed along to the next hill.
You also need to ask, how far did everyone go? It's not unusual for me to get passed after 45 miles when I'm taking the last 5 miles easy. Funny how the passers look crisp and clean, while I'm dripping sweat. How far had they ridden when they passed me?
A single sport touring bike is between. Not too much difference in frame, but the wheels are intermediate in weight. Or you could get a touring bike and a pair of light wheels, ride the light wheels, and swap out for touring. You'd freak the group members by riding that HEAVY bike, especially when your fitness improves to the point you're keeping up with them.