I'm approaching 8 years on the stock battery and although it has served me well, I think the time is near to retire it. It's never given me problems, and even survived my dead alternator episode from a year ago, but I don't want to push my luck anymore.
Tonight I had to leave the ignition switched to "on" (without the car running) while i was doing an OBD2 scan and after about 5-10 minutes the low voltage warning on my power invertor sounded (recall that the DRL's were on during this time). And sure enough when I tried to start the car it cranked slowly.
I think I'm going to go with the Motorcraft, based on what others have recommended. And who knows, maybe I'll get 8 years out of the replacement as well.
Oh and in case you're wondering, my car's only been garage-parked for 2 out of the 6 winters that I've owned it.
I figure it is bound to die soon given its age but for the last 2 winters it would take a lot to crank over but it would get the job done none the less. It just doesn't want to die. 
