We all like to shop for skis, at least I do, even if it is often just window shopping. It's fun, plain and simple. Skis, however, should be an after thought. Boots with a custom or semi custom footbed is where you should invest your time and money.
I just finished 3 days learning the nuances of ski boots and how to fit them properly. While I knew many of the key principles there is always more to learn.
The foundation of skiing from an anatomical perspective are your feet. This is true on several levels. First is comfort. A ski boot that is wrongly sized, poorly fitted, or perhaps just the wrong boot by way of flex will lead to a miserable day. Secondly, the wrong boot will lead to a loss in performance. Your feet are the vehicle through which all your motions are transferred to the ski.
This is where the footbed comes in. If you have a footbed that is shaped correctly to your foot you will find that many of the pains people associate with ski boots are resolved. The stock liners are nothing more than a thin piece of foam. This does not support your foot and does not lock your foot into place and can often lead to pain and injury.
With a footbed you will be better supported and you will be able to transfer energy to the ski which in turn will respond the way you want. It may sound simple but it can create better skiing posture which will lead to better turns.
The long of the short of it is that every ski boot should have a footbed that is fit to your foot. I even recommend them to people who are renting skis and boots for the season. The difference you feel will be significant.
Do yourself a favor and take the time to get boots that are fit correctly and add a footbed to it.