ALl i can say is that during testing of the REDUX campaign I can recall no issues with this mission, particularly of the drastic nature you report. I also cannot recall anyone else having such an issue.
However it was a smallish test team and probably didn't include your exact hardware (which is on the low end ).
As yu say, it is weird for a mission to give 1fps- it is certainly possible to make missions that can bring any rig to it's knees (i have one with 70 he111's and 200 fighters escorting-runs at 5 fps
),
in this case the mission does have more statics/stationary objects than previous missions in campaign- tho later ones can have even more! and even this number is nothing compared to some missions people have created with several 1000's of statics
- I wonder if this might be what is stressing your rig?
One possible test would be to run task manager (cntrl alt del while running the mission and look at the performance tab should show if it is a cpu or memory issue?