Having the plus sign jump around in the windows calibration box is a bad sign. By moving the dead band in the game your in creasing the box size around your stick where the "movement" is dead. Picture your stick is the center of the box, while the full throw you make from corner to corner describes the outside edge of the box. As you increase the dead band you create a box where the stick movement is reported as dead, or no movement. With your set at 40-50% you have a pretty big area that isn't responding.
I've only messed with Saitek stick, and seeing its still pretty new haven't had any trouble with it so I can't say whats in side of it. Taking the stick apart and cleaning a lubing it could help it, it would be the first thing I would do. After that it may just be time for a new stick. Having the plus sign in the xp controls window bounce around like that means it isn't reporting the stick movement accurately either due to dirt, dust, or just worn out parts. If it was solid in xp, and sloppy in the game then a profile might help, but with it being so bad in xp too I'd say it was the stick.