Q6600 Overclocking voltage

You can get away with 3 GHz at stock clock (I've set my Q6700 to 3.2 GHz at stock settings and it booted just fine). So in that regard, your voltage should be fine (run an OCCT test if you want to be 100% sure.). Your motherboard's northbridge will probably increase in temperature if overclocking, especially with passive cooling, but it should be all right as long as your board was made for it. Your temps look fine, but getting kinda high for my tastes. I'd suggest getting an after market cooler. I bought an OCZ Vendetta cooler for $35 and I've been pleased with it so far.