I bet there is someone on here with the type of bike you are interested in who would meet up for a ride if you ask.
Some people seem to be able ride anything, others are really sensitive to set-up, geometery etc.
I would test ride and bear in mind that you really need to ensure the geometry and size is correct for you and the type of riding you want.
Things like bars, stem, saddle, tyres etc will make a difference but they are cheap to swop. Unlike finding you have the wrong size frame, or its shite at climbs for example.
Why do you want a boutique bike ? Why not just buy a bike that rides really well, after all thats what they are for. Or do you just want to look cool in the car park 🙂