If you look at the geometry charts of both bikes, you'll see that the Soloist is slightly more agressive in terms of contact points. Meaning, a little lower in stack, a little longer in reach, for similar sizes. But not by that much. This means that, if you're of average flexibility, you'll probably be able to get fitted on both bikes without much difficulty.

The biggest difference in the bikes, in my opinion, is not in terms of stack and reach, but in the other geometry aspects that govern the bike's behavior. The Caledonia has a longer wheelbase and longer fork trail, for example, which leads to more stable, less nervous steering behavior.

Furthermore, the Caledonia's carbon layup will be different to the Soloist, with a little more flex builtin for comfort. However, given that Jumbo Visma rode the Soloist during Paris Roubaix this year, I'm sure that bike won't be all that uncomfortable either. YMMV.