Low Latency Doesn't help that much with P4s. Dual Channel does help quite a bit though, but of course you'll need 2 sticks <i>and</i> a motherboard with a chipset that supports dual channel.
You'll probably get better performance from 1gb of cheaper high latency stuff than you would from 512Mb of LL expensive stuff, but it depends on the application. - e.g. modern games really like lots of RAM, so even though your RAM is quick it'll be constantly paging stuff to and from the HDD.
What mobo do you have?
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