Even with a modded VBIOS I was unable to overclock over the 135Mhz threshold, things would get weird (artefacts, shaky screen, even bluescreens), with that setup best way to do it for me was finding the best way to cool the computer and fine-tuning the memory overclock to its max if you can find a VBIOS that allows you to mess with the power profiles you might just be able to push over the 135Mhz because that's the limit I was constantly hitting. I found the best way was to change to another MXM module with a faster and less workstation oriented tuning. I went with a GTX 970M, it has a lower TDP and overclocks better than the Quadro. You can even find GTX 980M but I feared the single fan solution would have gotten a bit overwhelmed with all the heat that would make, and I wasn't able to get a GTX 1060.