The King Arthur bread flour is a step below the King Arthur Sir Lancelot (KASL) high-gluten flour in terms of protein and gluten content. It is not the same thing as the Sir Lancelot. I will be shocked if you come back and tell us that you found a high-gluten flour at the retail level. It would have to have around 14% protein to qualify as a high-gluten flour. The KA bread flour is at 12.7%. King Arthur does not itself sell small bags (3-pound bags) of the KASL at the retail level, only by mail order and using Amazon.com and possibly a few others.
How long a dough will last is a function of a lot of things, including the recipe you are using, the amount of yeast, the amount of water, the finished dough temperature, and several other factors. However, under the best of circumstances, about the best you are likely to achieve is around three days, and that is under refrigeration. Occasionally some of our members have been able to get four or five days but that is not the typical case.
Dough can be frozen. There are preferred ways of doing this, but it certainly can be done and you should be able to get fairly decent performance out of it once it has thawed (and it is not too old). Given a choice, however, I will always choose making and using a fresh dough over frozen dough. Yet, frozen dough does have its place. It can be made to acccommodate time and scheduling considerations and also if there is leftover dough that might otherwise be thrown away.