You've been so outspoken against swaying that I think you'd really beat yourself up if you did that and ended up with boy #4. I thought I remember you saying you swayed for all your boys. Is there some different method you're going to be trying if you sway for #4? I don't know about you, but I always keep in mind the old saying "the definition of insanity is doing the same thing and expecting different results." Of course you could end up succeeding even if you sway exactly the same way, you know it's all an odds game, but still, I don't feel comfortable doing anything that failed before unless I make significant changes to the method.
High tech not working again is a major possibility, and a cycle of PGD/IVF is at least three times as expensive as MS/IUI. How many cycles do you think you'd even be able to try? Everyone else is saying wait, but I think a lot of people on this site have this mentality (especially when comparing it to MS/IUI) that PGD/IVF is the easy definite answer, like going to the baby store and handing over a check for fifteen grand or so and saying "One girl, please." That's so not the case. You could just as easily walk away with nothing to show for it but twice (or more) the debt you racked up with MS/IUI.
I'm not saying you should wait, but I'm not saying you should go ahead and ttc right now. I think you should think about it long and hard before you make your move, especially if this is your last baby.