There are many factors you should think about when buying spd shoes. What you will use them for, how much you want to spend on them, will you be likely to do a lot of bike carrying, what kinds of weather you will ride in, do you need arch support inserts etc. Above all comfort should be key as different manufactures fit and sizing will differ. Some will come up narrower than others so it would be wise to try as many as possible if you can. I have quite wide feet and a lot of shoes come in quite narrow for me. Also if you are likely to be walking any amount of time stiff carbon soles can be uncomfortable and you can't always tell this in the few minutes of walking in the shop.
I currently use specialized comp shoes. I think they are a good balance for my type of riding. They are very secure with two velcro and a ratchet strap and don't have a carbon sole so I find them a bit more flexible and comfortable when walking but not too flexible when riding. Stiff carbon soles will be more efficient when riding but I'm not a racer.
Specialized also do a variety of footbeds to get the correct allignment for your feet. I'm not a specialized rep by the way, just giving you my experience lol
I think buying cheaper shoes and then buying more expensive ones afterward is a false economy, you may as well get what you need from the start particularly if you have got the nice new xtr trail pedals. I was thinking about getting a pair of those myself.