would this be overkill?
Depends what they are. I often include standard deads and a stiff legged version in my back off work to rinse my mid-lower back. It also depends on what sort of volume you're doing on each.
You're not really giving anyone much to work with here...
No, it's not overkill. Abusing it could be overkill.
on Wendler routine I did classic deadlift in 5/3/1, and Stiff Leg DL in 5x10...
but on normal split I also did smth like - classic heavy DL at the beginning of back workout, and light SLDL at the end, with Pulldowns & DB rows in the middle.
It was fine for me. I regenerated well.
It always comes down to recovery ability, and volume/intensity being done.
This question sort of makes me think of a way Synergy designs some of his workouts--he'll have a lift that he's weaker on than another, work up to a maximum weight in the former, then seamlessly transition to the next lift with the heavier weight.
Now, this is something he would need to comment upon, not me, but just to give you a conceptual example, let's assume you were rack pulling more than you were deadlifting. You could deadlift up to whatever weight you're trying to hit for however many reps; then, go to a power rack, set the pins and start rack pulls at the weight you left off deadlifting. One possible justification for this physiologically might be that the CNS doesn't need to "recover" so much as seamlessly adjust to a new load. I.e., it doesn't think, "Hey, I'm doing a new exercise," so much as "Hey, the load has increased."
Again, none of this is endorsed by Synergy unless he were to come on here and say that I'm on the right track. It's just something he does that I noticed from his logs.
No, it isn't.
I would personally much rather use a deadlift/good morning combo as opposed to a deadlift/SLDL combo. That's just me though.
I wouldn't but then again when I deadlift I go all out, so I know I won't be able to do another variant for at least another 3 days