i brought the same spec diff company and my pc just diddnt like it. either it crashed or it wouldnt register so what about this...http://www.overclockers.co.uk/showproduct.php?prodid=MY-301-CS&groupid=701&catid=8&subcat=1392 ?Personally, I would suggest selling on your existing kit and buy this one instead. It doesn't cost much more than a 6GB 1600MHz kit and will put much less strain on the memory controller of your CPU (since it is only running 3 modules instead of 6).
That said, may I ask what you use the PC for that requires more than 6GB of RAM (the vast majority of games these day's can only just make use of 4GB)?