Thanks for working on performance! Here is some information I collected using your -O3 ISO.
System:
Tiger Lake Core i7-1165G7
System76 Lemur Pro 10 with 40GB single-channel RAM
Samsung 980 Pro 1TB NVME drive
All tests performed on ZFS with ZFS-native encryption
Compiling the Chapel 2.1 compiler:
347.42 seconds CachyOS x86-64-v4 and other optimizations
401.36 seconds Noble -O3
420.10 seconds Noble without -O3
Running the Chapel examples:
361.44 seconds CachyOS x86-64-v4 and other optimizations
367.39 seconds Noble -O3
387.37 seconds Noble without -O3
So, for this workload, -O3 improves performance by an average of about 5%. (CachyOS adds other optimizations on top of that, adding an average of 8+% in performance.)