You need to take your driving style into consideration here. The tire Nazi's that are assailing you are just that; they are pushing a set of specs on you that are more of a rule of thumb than anything else. You can do just fine with W- or Y- rated tires on your car, though I personally wouldn't go below that (except for dedicated snow tires, which you're nuts if you're doing above 80MPH in).
I'm running W- speed rated Bridgestone PP S-03 tires now and actually have better traction and handling characteristics with them that I ever did with the stock Z-rated BFG KDW's...
As far as the idiot from DirectTire, lower speed-rated tires usually have a harder compound than higher speed-rated tires do, so 9 times out of 10 the lower speed-rated tires last LONGER, given the same type of driving.
I'd go with the Pirelli's at Ford. The "buy one get one free" and the warranty is a pretty darn good deal (you are actually paying for that 4th tire through the uplift on the other 3. Check Tire Rack's prices on the Pirelli 7000). Regardless, I'd go with it, just for the warranty, though read it carefully and make sure they don't have loopholes in it big enough to fly jumbo jets through...
