5x1600m is a classic. I've done those workouts before and they do get the job done. I've also found that adding some 400m repeats at the end can help with that extra kick at the finish. Nothing fancy, just good old-fashioned hard work.
PF is a nightmare. I've had it a few times and it's always a battle. I've tried night splints, orthotics, you name it. What's worked for me is just taking it easy and not running for a bit. Sounds obvious, but it's hard to do when you're used to being out on the road/trail. Also, try to lose some weight if you're carrying extra pounds. That seemed to help me too.
Yeah, it's tough to break the habit. I had to consciously focus on my foot strike for every single run. It's annoying, but it's all about building new muscle memory. I also found that running on trails or softer surfaces helped me transition to midfoot striking. Less impact means less heel striking, I guess.