For sure, you should take the kind of fabric you sew on to the shop and try sewing/fmq on it with the different machines you are comparing. You might be surprised how they feel once you actually are sewing on them. If you use different threads, bring them along too. Silk or a heavier weight thread might act different in the machines.
I'm planning on purchasing a new machine in the next year or so, so I've been doing some research too. Good Luck!