Well, I got the Yoko Avid Touring S tires today. They are fantastic! I've had some time driving it around on wet local roads, and also some time driving it on moist highway (enough to cause a little spray).
Even with the spray on the highway, these tires are much quieter than what I'm used to with the Dunlop SP Sport 4000 A/S tires.
They do feel a little bit softer, but they handle very well. You turn the wheel, and it goes! Accelerating from a stop on wet pavement is okay--better than my bald Dunlops, but it's still difficult to get going on certain tight right turns from a stop sign. However, I expect this to improve as the tires get broken in (I'm not sure, but the stickers may have been left on the tires, causing this issue).
Braking is fantastic in the rain. Where my Dunlops would have already engaged the ABS, the Avids were gripping the pavement like mad!
Conclusion: I have never tried the MXV4 Primacy, but people say that these Yoko Avids are Michelins for half the price. And from what I've experienced so far, there is no reason to dispute that. If you're thinking about getting the MXV4 but don't want to pay top dollar, give these Yoko Avid Touring S tires a try. I don't think you'll be disappointed!