In the standing barbell curl, I use 25-10-25 but I don’t make 10 at all in 25 seconds. Imagine doing barbell wrist curls truly at 30-10-30! Sort of the reverse of doing 240 degree ranged machine pullovers where 30 second negatives for me is almost perfect but the middle 10 is a problem since I’m not a ballistic kind of kind person except in martial arts. 
On the curls focus and use a lighter weight until you get the hang of it. If after a few weeks you find it is to much time lower the time on the negatives.
Note in Dr.Darens book he uses hammer curls when using dumbbells. I would not do regular DB curls at that speed for the reasons you have noted.
With the pullover I would try what Dr.Darden said. Or try 30/30/30 thats 90 seconds.
Personally if you have not bought the last two books that Dr. Darden wrote I would do so. You can still apply not to failure workouts. DB hammer curls are on of the exercises.
Something that helps me focus is to write down a routine and stick to it for a while.
I found through trial and error the exercises I do the best. I found through trial and error the best rep speeds that work well for me. I do like 30/10/30 a lot. But most anyone works for me.
I keep records of my workouts.It’s nice to go back a year or two and note changes I might want to make. Better yet set future goals.
I just got done re-reading Nautilus Bulletin #1,Living Longer,Stronger,and Upside Down Bodybuilding.
You might find a nugget or two that you can apply.
I haven’t written down my workouts in a long time but I’m starting to do so again so I can see if I’m actually progressing at all at least with weight or repetitions. I can’t tell anymore by just looking at my muscles.
Scott
I find that doing hammer strength bicep curls, arms up, one at a time…i get better bicep workout than BB curls with 30-10-30
I’ll have to look up what a hammer bicep up machine looks like?
Scott
