Hmm. Did you set all cores to 3.8? If so, that may be the problem (I don't KNOW that, but it would make some sense).
Just looking at it (and I didn't know this, actually), 3.1 should be the stock 4 core Turbo speed, as well as the stock base speed (it goes 3.4 for 1 core, 3.3 for 2, 3.2 for 3, and 3.1 for 4), so 3.5 would be what the OC'd 4 core Turbo should be.
OK so I figured it out -- there was a setting in CPU power management that I effectively disabled, and the board wouldn't go turbo.
This particular board is weird. Running stock @3.1ghz the chip is only pulling 1.18v at full load. When turbo kicks in the vcore goes to 1.3!! This seems high as my other unit (2500k) runs 4.2ghz @ 1.24 vcore.
This 2400 should be able to run at 1.2 and still hit 3.5 ghz, but the motherboard won't let me adjust the voltage. It seems to only want to run full turbo mode on its own terms (which is 1.3 vcore).
Maybe its these quirky asus bios settings, but I can't figure out how to lower the turbo core voltage and maintain full turbo speeds. There is a setting that allows me to adjust the power, but it is measured in watts instead of volts (?!). When I do decrease this power setting the motherboard won't go to full turbo.
Thanks for the help -- yes I was finally able to access offset mode but I had to disable some sort of power saving mode for it to even show up as an option.
Turbo is running at 1.2v now. The cpu peaks at 3.6ghz, when running p95 (it switches between 3.5 and 3.6). I thought you could only go up four bins with this chip when running all four cores (i.e. from 3.1 to 3.5). Must be a glitch in the intel turbo boost monitor software.