I think I have troubles with the beginning of my deadlift movement. My lockout weight numbers are fairly high compared to my regular DL, and my deficit DL is pretty low, so I think it might be good to do more deficit deadlifts..
I was thinking of doing 5x5 for deads on a deficit for 8 weeks straight, instead of doing 5x5 for the regular deadlift.
Would that be a smart thing to do? Or would my technique on the normal deadlift get worse by not practicing it for that period?
Start with a 3" deficit. A jump to 4-5inches may be too much, it depends on your build and flexibilty.
One way that has worked for some is to start on a 1" block with a weight that is reasonably heavy (i.e. not a gut buster) off the floor and add another 1" block each week, keeping the weight the same, until you get to 4 or 5" then add weight as you remove the blocks 1" a week until you're back to floor level. Then see how you go.
Deficit pulls are a great training tool. Not only do they help those that are weak off the floor, they also help those that stall in the usual conventional puller sticking point (just below knees). I find a small deficit- such as standing on a standard 45 lb olympic plate works best.
A greater deficit changes your groove too much. I have usually done these for singles or doubles- with the emphasis on being explosive with either max weight or light (60-70% of max) speed work. But I don't see why you couldn't go with 5s.
Start of a deadlift is mostly quads and glutes, which front squats will make "cock strong".
As for pulling from a deficit, don't pull from more of a deficit than you can get in position for. If you don't have the flexibility or if it's different form than how you'd pull from the ground, carryover will decrease. Even standing on 1 plate would probably help build even more strength from the floor.
If you want to get scientific about it, a movement can be strengthened up to 15 degrees ROM outside of the motion trained, so if a 1" deficit is within this 15 degrees, you'll be strengthening the start. Even if you go outside of it, you'll still be strengthening that portion since you'll be going through that point, but not as if you were within those 15 degrees and starting the movement.
If you want to get less scientific and just get stronger (I tend to lean towards this option), pick a deficit height you are comfortable with and pull, get stronger, and cycle the exercises Hanley said.