Hello, I own a Motorola Defy Mini XT320 (MSM 7225A-1 Chipset)
We overclock using the PLL2 overclock and one of the XT320 users and some HTC Explorer users have burnt their NAND.
Here's an explanation why this happens:
PLL2 overclock can be compared to FSB overclocking in computers i.e locked multiplier overclocking in the BIOS. FSB overclocking involves overclocking of the PC buses such as the Memory Bus, PCI/ PCI-Express bus and AGP buses (older computers) and the CPU. It works out by XXXXMHz multiplied by X multiplier and that will give the CPU speed. PLL2 overclock does the same thing because PLL2 controls the bus speeds (exists in the SOC). It overclocks the memory buses, SOC clock, internal storage (database IO) speed and of course the CPU. It works out by XX multiplied by 19/2 and that gives the CPU speed. That's why PLL2 on 800MHz is faster in performance than PLL4 on 800MHz . Therefore that's the reason why people complain of burnt NANDs on HTC Explorer and Motorola Defy Mini XT320/321.
PLL4 overclock can be compared to unlocked multiplier overclocking where you adjust the multiplier in the BIOS and it will automatically adjust the clock speed depending on the multiplier of the CPU. Therefore this only overclocks the CPU. PLL4 overclock only overclocks the CPU and NOT the buses so it can go at much higher frequencies than PLL2 overclock. PLL4 overclock does NOT adjust bus speeds so therefore it is much safer to overclock and it doesn't burn out your SOC.
Dunno why Qualcomm disabled it in the MSM7225A chipset, probably to avoid people overclocking.