I have 2 128 ECC 100 DIMMS and would like to upgrade. I am looking to go to 512 with the possability of 1024. First should I go to the 256 DIMMs or fill all my slots with 128's and change it later? Next are the ECC 100 worth the extra $200 per DIMM compared to the plain PC100? If I went to 256 should I get the ECC 100 or PC100?