How much a performance gain should i expect to see?

The performance of a system depends mainly on the following items. Processor clock speed 3.4 is much enough for normal use. Second comes the display ram or graphar card more the display ram more performance you gain. As you have not specified your use with the computer i do not have a recommentation in that, any way 1 gb is fine. With 1 gb display ram and 1 gb ram system will be a real blade for you