^^ Buddy, I don't think you understood a bit what I've said. For running Ram @ 800 MHz DDR speed, you don't need to set the FSB to 1600 MHz.
If F is the FSB Speed and M is the Ram Multiplier Value then you have to set their values according to the given equation.
F X M = 800
Intel use Quad Pump FSB, so 200 MHz Base clock speed means the effective speed is 800 MHz. The CPU Multiplier for E5400 is 13.5 (200X13.5 = 2700). The main problem with these older motherboards is that they don't support Intel XMP profile and the Ram speed is needed to set manually and that limits going beyond 1333 MHz speed for the Ram.
Here are certain links which might be useful:-
*kimoechan.wordpress.com/2012/05/06...0-and-p5g41t-m-lx-part-1-building-the-system/
*www.tomshardware.com/forum/269954-29-overclocking-asus-p5g41t
gyanbhartip, could you provide the memory or DRAM settings available in the BIOS?