I think this issue is due to your new OS installation, and specifically your Windows Power Option, or power plan. It sounds like your power plan is set to Balanced, as it is by default. With Turbo disabled in the BIOS, and not using the High performance power plan, the CPU speed won't reach 4.2GHz. Your SpeedStep and C1E/C States settings in combination with the Turbo setting may also be influencing your OC level.
BTW, when using your board and CPU, it is impossible to have Intel Turbo Boost disabled and CPU Ratio set to All Cores at the same time. You can set Turbo to disabled if CPU Ratio is set to Auto, but if you then change CPU Ratio to All Cores, Intel Turbo Boost changes to enabled.
The way that Sandy Bridge and Ivy Bridge CPUs are over clocked is not the same as the earlier generations of Intel CPUs with locked multipliers. It was a common procedure to disable Turbo on the earlier generation CPUs, and increase the BCLK and CPU voltage to OC. SB and IB CPUs must have Turbo enabled in order to increase the multiplier, which is the main way to OC those CPUs.