i have a dell E510 with 4 slots that can max out to 4gb of ram. All then slots can be dual channel ram. Right now it has the factory dual channel 256mb of ddr2 pc2-4200 for 512mb of ram. Since it has dual channel of 256 in slots 1 and 3, i want to put 2 gigs ram in slots 2-4, which are the dual channel slots left. Do i get 2 more gigs of of pc2-4200 or get the fastest it can take the pc2-5300? Thanks