It worked really well to be honest. 45L on my bike and 25L on my friend's bike... and we both agreed we seriously overpacked.

I might even be able to get camping gear in mine next time. We went from hotel to hostel this time because he didn't want to load down his road bike with camping gear.
And if that isn't enough I have a lowrider and small panniers I can put in the front.

This was our initial plan, though we did deviate a bit, but ended up doing 740 km (460 miles) and 6821m (22378 ft.) of climbing in 9 days of riding with some days of walking around the city in between.