Dave posts slightly off-topic video's like lab experiments and such in his eevblog2 channel:
The Q6600 is/was a very decent CPU (I still ran it as my main machine ~2 years back), and I still know people who run it and use it to play modern games on it.
However, it is quite a bit of a TDP monster (105W). So I wonder too if the system is rated for it.
PSU is 250W:
http://us.shuttle.com/barebone/Models/sd30g2b.htmlList doesn't say Core 2 Quad, only Duo. The E6750 is a 65W TDP CPU. The Q6600 is almost double with 105W.
If you take 105W CPU + 50W motherboard/graphics + 30W hard drives, it's about 200W peak load. That's quite insense for a 250W PSU.
Also, the heatsink seems a bit undersized. Luckily, if the CPU starts to run hot it will throttle back, which will inevitably cause performance problems.
So it may work, because chances are the motherboard in that PC is capable or doing more, but I wouldn't be too surprised if any stability issues would come along.