Getting footwear without trying it on first is a pot-luck exercise, and I would very strongly recommend you don't do it.
Your feet are a complex 3d shape and for maximum comfort and effectiveness you'll want something built on a last pretty close to them. Feet, and most manufacturers' lasts, are different shapes so you'll have the best chance of finding the right ones by trying them on in person.
No matter how whizzy the technical features are, if they're the wrong shape for your feet they'll be a bad buy (for example, on paper Inov8 Flyrocs are the absolute perfect shoe for some of my requirements, but on my feet they're simply not very comfortable).
So don't decide what to get until you've tried a pile on is my advice.
Pete.