Worth driving two hours to try packs on, or do you all order three and send two back?

Two hours is worth it once, not for the bag but for the fitting. A shop with staff who know what they are doing will measure your torso, put twelve kilos of weight bags inside and let you walk around for ten minutes, and that tells you more than any review. Once you know your torso length and which harness shape suits you, ordering online afterwards is low risk forever. Go, get measured, and feel no guilt about buying elsewhere if the price is silly.

Push back on the fitting mattering for what you are describing. Torso length and a load-carrying suspension are decisive when a pack is heavy and you are wearing it for six hours on a trail. For a 35 to 40 litre travel bag carried between a train and a hotel, most of those bags have a fairly flat panel harness with limited adjustment, and what will actually determine whether you like it is the opening style, whether the laptop sleeve is accessible, and whether it stands up on its own. Those you can judge at home.

Whatever you do, test it loaded with your actual things rather than the shop's beanbags or an empty bag at home. I ordered a bag that felt lovely empty and discovered that with a laptop in it, the whole thing sagged away from my back and the shoulder straps dug in. That only shows up under load.

One overlooked reason to see bags in person: dimensions on paper are close to meaningless for whether something fits a sizer. Two 40 litre bags can be very different shapes, and the one with a curved top is the one that gets waved through.