So I've been riding the 1.2 preset in the DX/D2 Overclock app and it's been entirely stable, but it's a wonder how that little .1 difference between clocking at 1.2ghz and 1.3ghz makes in performance.
I've still had little to no luck with any recommended voltages at 1.3 - but I'm seeing some folks report stable profiles at as high as 1.4, is each device really that different or am I just barely missing something crucial here?
Yes, each device is different. I believe in that thread I linked to earlier, he talks briefly about the fabrication process and gives a link to an article that explains it in detail.
In a nutshell, if you do a fabrication run that nets 1000 chips, you could potentially have 1000 different maximum settings.
On my old Droid 1, I could never get it stable over 1.2GHz, even at High voltage, even though some people could go up to 1.4GHz with Ultra-Low Voltage. I could also never get any ULV kernels to work at all, even at the stock frequency.
With my Droid 2, I'm stable up to 1.35GHz ULV, but once I go to 1.4GHz the entire system becomes unstable and apps crash all over the place. I haven't tried to see if I can go faster at a higher voltage because I don't actually have my phone overclocked, the extra .35GHz doesn't make enough difference in my daily use to justify using it.
I've even seen someone with an OG Droid that couldn't go over 600MHz even at High voltage or the system would just freeze and boot loop.