How do I test to see if my CPL number is good enough?

You should generate the lead first. Then follow up on them via email with your sales page.

Yes - let's say that.

In fact, let's say that it runs for much longer than that, which would almost certainly be better?

Relatively simple: become your own affiliate, and then use different ClickBank affiliate TID's for the different purposes you want to test?

(There may be other ways of doing this, too, but that's the easy one, I think. I seem to recall that the last time this question was asked, there were a couple of alternative ways suggested too, but the discussion became very technical and very complicated pretty quickly, and without my being able to understand it, myself. I think the above is both the "quick and easy answer" and the "normal answer", anyway).

Yes, I see. Well, they do say it's always right to test everything. Have you thought about maybe including in the test, also, a version of the sales page with an opt-in on it as well as a sales page and a squeeze page? I ask because I'm guessing - albeit knowing absolutely nothing about your product, niche, traffic or local weather conditions - that that could possibly be the most profitable of the three? Which might be of some value to you? (Though clearly, no successful affiliates will be willing to send their traffic to any page with a vendor's opt-in on or attached to it, whether it's a squeeze page or not. But that might not matter? You might still want to use one just for yourself?). It does seem pretty much unimaginable that not even trying to collect the prospective customer's email address could possibly be "the winning line", surely? (Decent affiliates, of course, will understandably want, need and expect to do that themselves, and can hardly be expected to tolerate the vendor doing it for them).