I've used 3/4" inch Plascore for years. I bought a dozen sheets, then bought to more from a customer who bought too many. I'm down to my last few sheets. Next time I'll at least consider 1" thick Plascore (or perhaps air-comb).
The thicker it is the stiffer it is and 1" isn't much heavier. For Stressed Skin Panels (what this ends up being) stiffness increases as the SQUARE of the core thickness, so a small increase in core thickness makes a big difference in stiffness.