Although many E7500's will run faster than 4 GHz, your motherboard is going to limit you to around 3.7 GHz.
The G31/G41 chipset is an economy, entry level chipset. Unless you get really lucky, you will not be able to push the FSB freq past about 360 MHz. I have a G'byte G41 board. FSB freq of 352 MHz works. 353 MHz doesn't.
CPU-Z is showing your CPU running at 1.6 GHz under idle conditions. When the CPU load increases, the CPU will go to full speed automatically. It's called SpeedStep.
This should be your first stop.
Core2 Overclocking Guide (generic guide based on one of the Sus boards.)http://www.tomshardware.co.uk/forum/259899-11-core-overclocking-guide
Do not exceed 1.45 volts core voltage or 70 C load temps.