Wise and considered words to help steer me. I wonder if OCLP has a setting which can slow the boot process down, rather that my verbose mode work-around? Anyway, it may be timely for me to reflash my Matt Card with the reconstructed ROM done expertly by tsialex, as the ROM chip registers may just be getting a bit full or have conflicting drive cache settings, seeing I boot in and out of 10.6, 10.12 and 12.5 regularly. Starting with a clean slate may give me a better rate of successful Monterey boots - seeing few, if any, other 5,1 users have reported boot problems (baring the boot loop issue which I haven't experienced).
[Update] I reflashed my ROM chip but am still getting boot stalls at about the 1/3rd way point. I'll add -v to my OCLP boot string until a better solution comes along. I'm still incredibly grateful to have my 5,1 running so well on the latest OS.