|You didn't tell us anything about your RAM or motherboard?|
For best performance, you should be maintaining a CPU:DRAM frequency ratio of either 1:1 or 1:2. Which ratio you use depends on the RAM. If you're running the CPU frequency at 400MHz, you should either be running the RAM frequency at 400Mhz (DDR800) or 800MHz (DDR1600), whichever your RAM is capable of handling. That means you may have to underclock the RAM.
With the right board, RAM, & CPU cooling, you should have no problem running the Q8400 at 3.2GHz (8 x 400MHz). Just make sure to lock the PCIe at 100MHz, disable all Spread Spectrum settings, disable SpeedStep (at least temporarily), manually configure the memory settings to maintain the optimal ratio, & adjust voltages as necessary to keep everything stable.
"...but i also dont want to unnecessarily endanger my hardware..."
Overclocking will NOT damage hardware unless you increase the voltages beyond reasonable levels. Intel specs the Q8400 voltage range as 0.8500V-1.3625V.