I'm not sure if this will work with intel but with amd, its been found that if you lower your fsb's speed you can also get a higher oc.
I don't know if the same goes for intel, I've never gotten a chance to mess with an intel motherboard with an unlocked bios.
Actually, with the 1156 and 1366 sockets (i3/i5/i7) they did away with FSB. The new setup is you have a base clock, and from there a CPU multiplier, RAM multiplier, and QPI Multiplier. Generally for CPU you get 9-21 multiplier, and beyond that only with Turbo Boost although I think the i7 980X has completely unlocked multipliers. For RAM you get 10, 8, and 6x and for QPI I think it's 34 and 36x.
In that regards, using the lower QPI can make higher OCs easier, and sort of the same with base clock although it's hard to say if it's the base clock or the final speed that will cause the biggest problem.