Laptop, and extreme CPU. HP and Dell block TPL/TRL adjustment even for XM processors, and HP took it even further with their 1333 MHz limit on RAM. I have 1600 MHz sticks that can run fine at 1866 and probably more (tried with Thaiphoon Burner), so that's really annoying. I don't want an Alienware to get that.
And BCLK allows for a 5MHz overclock, which is not much, anything more and the system crashes. Which is really strange, may have something to do with PCIE as Dogma said.
I just want to get everything out of my extreme processor and RAM.