It's true the G3258 does not support Turbo, and I've seen ASR BIOS updates that included removing the Turbo option when the processor does not support it.

But when I disable Turbo in my board's BIOS, I no longer see the CPU's speed displayed above 3.2GHz, when I have both multipliers set to 40. The main BIOS screen will show the CPU's speed as 4000 MHz, but everything else displays it as 3.2GHz.

So I did some stress testing in IXTU, with the multipliers set to 40, and with Turbo enabled and then disabled.

CPU Speed Max VID Max CPU Temp Max TDP Turbo Multiplier
4.0GHz 1.120V 56C 27 Watts Enabled 40
3.2GHz 1.022V 48C 17 Watts Disabled 40

Asrock Z97M OC Formula multi not kickin in-xtu-g3258-turbo-png

In the upper right of this screenshot, we can see that Turbo is disabled, and the multipliers are set to 40. The lower area shows the CPU Speed (Processor Frequency), VID (CPU Core Voltage), CPU Temperature, etc.

IMO, it is clear that with Turbo disabled, the CPU is running at 3.2GHz, with the multipliers set to 40. The maximum VID, CPU temperature, and TDP are all lower than in the screenshot of my previous post, which shows the same settings but with Turbo enabled.

The display in the main BIOS screen which shows 4000MHz regardless of the Turbo setting, is wrong when Turbo is disabled. Even if it is correct when using the BIOS, once the OS boots, the CPU speed will be 3.2GHz when Turbo is disabled and the multipliers are set above 32.

All the hardware monitoring programs that display 3.2GHz with Turbo disabled and the multipliers set to 40 are correct.

Anyone can easily test and verify what their board/BIOS and BIOS settings do by using IXTU. Of course in your case you don't have the Turbo option available when a G3258 is in the board. You could use IXTU to see if Turbo is enabled, it might show that setting even if the option is not present in the BIOS UI.

My board with the version 2.34 Beta BIOS needs Turbo enabled to OC this CPU, the other BIOS versions will not allow an OC to be applied with the multipliers to a G3258 on a Z87 Extreme 6 board.