Deficit deadlifts should be rotated in for 3-4 weeks at a time, and should be done with weights less than what you'd pull from the floor. For every inch you add to the deficit, subtract about 10% of your max weight from the floor in the same rep range. So if you're doing 5 sets of 3, and your 3RM off the floor is 425 pounds, you should start with about 385.

Of course, this varies from lifter to lifter, so don't feel like you're automatically restricted to 90% intensity at a 1-inch deficit. If you can handle heavier weights, have at it. Just make sure you can handle the lighter weights first before jumping up.