Well, yeah, but it's reasonable to expect you to have that at the moment you first seriously ask this question. You having all that CAT5 is a reason to ask the question!

Besides, I thought the original question was more along the line of "am I doing the right thing for my customers and my business?"

Moving on a bit, if you had thought about this issue a year ago and had then decided to install CAT6 to lengthen the time before your new installations become obsolete, you'd have either totally switched or you'd have a mix of product so you wouldn't be able to make a point of how much CAT5 you have.

As for cost, yes, it's not a lot. Four cents a foot is $211 per mile. Is that a lot? How many miles do you use in your average installation? The price per million feet is misleading as it's still a small percentage of the price of a job. Besides, it's the million foot installation where you'd damn well better use the better cable, since so much more is on the line!