The FSB is not at the maximum of the motherboard, if anything it is at the theoretical maximum (for what it is designed for) but you can overclock. You should be able to increase it more, doesn't the BIOS let you do it?
If it doesn't boot up, it might be because by increasing the FSB you are also increasing the speed of the memory and you would have to play with a divider to reduce the speed of the memory as you increase the FSB, that or relax latencies or increase voltages, there can be several things but what is clear is that with a processor without an unlocked multiplier you can only increase by means of the motherboard bus.
Anyway, if you have already increased it from 2.83 to 3.4 it is not bad at all, from there you may need more voltage and better refrigeration. That there are people who have increased it to 3.9 or 4Ghz means nothing since you don't know with what motherboard/chip/refrigeration/voltages they have achieved it.
I would almost bet that you are missing CPU voltage and that probably from 3.4Ghz it will start to ask for quite a lot of voltage (it always depends on the luck you have with the chip).
Edit:
1.2-1.3V - for a FSB of ~400 MHz.
1.4-1.5V – for a FSB of ~420-440 MHz (exceed 1.4V at your own risk with a 45nm chip)!
1.6V – for a FSB of ~440-475 MHz - use at your own risk with a 45nm chip!You should be aware that newer 45nm fab chips are MUCH less tolerant toward high VTT than their 65nm predecessors. Anantech published their experience frying a QX9650 with high VTT’s as an example.
Vcc – Initially, set within 200-400 mV of where the auto setting used (remember that you need a little more in the BIOS compared to what CPU-Z told you). Remember to consult Intel’s processor finder to know where the upper-end of safety is for your processor (I believe the figures there correspond to the values CPU-Z is displaying, not what you set in the BIOS.).
DRAM – What ever the RAM manufacture recommends is a good starting point. Unless you’re really overdriving them, they shouldn’t need more.
SBCore – I’ve always used the lowest setting, but I typically don’t push my systems that hard (20-25 %). You’re on your own here.
NBCore – Start off low, 1.33 or 1.37 and see if you need more. Also, a little bit can go a long way. My system is unstable @ 1.330V here but stable @ 1.370V which is a difference of only 40 mV (0.04V).