Which RAM setting is best ?

[Sujit15]

Is it best to have 4x 1GB or 2 x 2GB of RAM?

This applies to when they are of same speed and the same Ram chips, only that it is 1GB or 2GB.

[Steve123]

This varies from memory to memory and also the motherboard to motherboard.

What motherboard are you having? What memory do you have (make and model)?

[Sujit15]

Motherboard: Asus P5N-D
RAM: want to buy new one

Either: 4 x 1GB - Kingston HyperX 1GB PC8500 DDR2

Or: 2 x 2GB - Kingston HyperX 2GB PC8500 DDR2

[Alexisus]

Fewer chips use less power and well decreases the load on North Bridge on the motherboard. You will not notice any performance difference.

[southparx]

Buy the cheapest PC6400 4GB kit you can find. Theoretically 4x 1GB is better than the other one, but you will never see the difference.

You will not notice any gains by going for PC8500 sticks then of PC6400 pieces if you do not take no bells your very seriously and likes synthetic benchmarks.