I have some PX 12 lifter mediums (90 mm brake) mounted on Watea 84s and also have PX 12 fluids on some Contacts. I really like the hold you get from this binding and have found that I can run a slightly lower DIN than I have with some other bindings.
I also own, but have not mounted the same PX 12 lifter wides from tramdock. When researching the PX lifters, I knew I wanted a low ramp angle and thought the delta was 2 or 3 mm. After seeing aschick's post, I just measured the mediums on my 84s and it looks to be 4 mm- I have a big foot and have not noticed the difference (but have only been on the Wateas twice to date).
I think the lifter adds 6 mm (a quick check says 6.5 on 1 site)- this means you would have a slightly negative delta if you took the toe lifter out, which might feel worse than 4 mm delta. Unless you know you want no ramp, I would tend to mount them as is first.