RallyMaster's OC advice gives you CPU@2.4GHz (3800+ speed), and a memory divider to keep the RAM in-spec (DDR400). The only thing will be out-of-spec is the HTT (900 if the 3xHTT multiplier is used in BIOS), and this doesn't affect system speed (HTT @ 800+ has never been found to be a bottleneck).
If you have overclocking RAM, you can run it in-sync (1:1) & gain a small boost in apps & games sensitive to memory bandwidth. My Crucial DDR500 is stable @1:1 with my 3000+ overclocked to 9x267 (2.4GHz), HTT 4x267. CPU benchmarks give identical results to a 3800+, except where memory bandwidth plays a part (giving my OC the edge).