Well, id much rather have a Seagate being as my Maxtor (even though it has fluid bearing) makes a whiny noise that is very noticeable over my "louder" 34Db Antec TruePower.
If you got the Low Latency HyperX that will not go well with the other sticks unless they have the exact same timings, so either the HyperX runs at lower timings or it gets overvolted because of trying to force the other sticks to run at the faster timings. Id just get another stick of 512MB HyperX being as RAM is so cheap right now.