I think that it is always best to wait until AF should show before testing.
The idea of testing too early makes me nauseous because I don't want to get that faint BFP, and then it not take and have to deal with a CP. I don't really want to know until it's real.
BUT, having said that (hahaha), I can imagine that if I have TONS of symptoms (but, of course, I would NEVER symptom spot!) that I would cave close to AF. The symptoms though, would have to be SO COMPLETELY out of the ordinary in order for me to want to check.
I'm scheduled to test on July 26th if I O around the 18th like FF marks me. If I O earlier, like it seems I might, then I'll move it up. That is IF I O.