What is the normal QPI speed on your motherboard? Check it and don't overclock the QPI, it's almost certainly that, and if not, in the meantime, review the basic overclocking guides.
Regards.
There's no complication in raising the CPU multiplier, but to raise the bus, you have to keep some speeds below their maximum, and that's done by setting them to manual and selecting multipliers that leave them at their normal speed or below.
I haven't touched modern Intels yet, so I can't clarify it directly for you, but anyway, your question is basic, the BCLK is the one that the others are multiplied from, and if you follow up, I'll write you a particular guide, so first, check the basics in the guides.
Regards.
P.D.: The northbridge is naturally another thing you have to control, with the basics you already do overclocking, it's not difficult, and in the guides they'll tell you the precautions you have to take.