I don’t own an S40, so I can’t give any experience to that, but I have done some bikepacking/touring on garbage roads and gravel with the Q45.
The Q45 rear shock is super nice for comfort, and reaaaally helps out when you accidentally send it over a pothole that you didn’t see.
I don’t know what your priorities are, but I have loaded up my Q45 for 3 days adventures so far, and haven’t run into weight capacity issues.
Looking at the Eurovelo route, that’s gonna be quite the ride.
Regardless of which you choose, I think getting extra racks for under the seat would be necessary.
Regarding your concern with weight, I’m not sure how much weight savings you will get. I just tested my own setup, and my Q45, with everything loaded including tent, sleeping bag, clothes, etc, is about 55 pounds.
When I take off most of the bags it comes out around 42 pounds.
I also think a lot of your gains are going to come from being a bit more aerodynamic than the trike, there is less frontal area, and only two tires contacting the ground.
There is definitely a learning curve with the Cruzbike system though, the front wheel drive has a unique steering experience. It took me about 3 months to get really confident to be able to ride at the level I was at on an upright bike.
All that being said, I love my Q45, so if you take anything away from this, you have at least one glowing review In the Q’s favor.