It all depends upon how much RAM you have on your computer, as, if the card needs a lot of memory to perform a certain graphics task, it will use some of the RAM and thus, if you don't have lot, it will result in your computer slowing a little, but not noticable.
I suggested the 256MB because the rest of your computer is only two years old and so you will get slightly better performance but for a decent period of time as your PC has plenty of life left in it.
dave
I suggested the 256MB because the rest of your computer is only two years old and so you will get slightly better performance but for a decent period of time as your PC has plenty of life left in it.
dave