For those of you who saw this in dual laser setup (Citywalk as far as I know), did the IMAX sequences take up the entire screen from floor to ceiling? I watched in Irvine on a single laser setup and while it expanded to quite a tall ratio it did not take up the entire screen such as Nolan’s 70mm IMAX films.

I don't think Single Laser venues do the full IMAX ratio as far as I'm concerned. BTW Over an hour of Dune will be in full 1.43:1 IMAX ratio.

Also, has anyone noticed the “speckle” effect on their IMAX screens where there is almost like a glitter/shimmer effect during very bright scenes. The desert scenes were very bright and I noticed this effect quite a bit which was very distracting. Thanks for any info

Yh, this is a defect of laser projection but it can be mitigated in some ways. It does seem a lot more common with IMAX laser for some reason. Dolby Cinema on the other hand barely has those issues.