Absolutely no contest OCZ, I have had all hell on getting a working set of Geil DDR2 6400 3 sets in all and then finally I sent them back to Taiwan and got a set back that works, that's about the worst testing before sending them out I have ever had, how can they test them before sending them out when so many are bad? I honestly thought I had lost the plot, I took 2 sets back to OcUK they tested them whilst I waited and both were DOA then the final set back to Geil who had the nerve to ask are they faulty or do they not overclock properly, after 30 mins of memtest I recieved an E mail that I would get a new set and in fairness they do work well up to over 900MHZ but I had driven 285 miles to and from OcUK then sent them to Taiwan in all taking 4 weeks to get a working set. For the money I could have bought the most expensive ram and it would have been cheaper.
But on the bright side whilst waiting I entered the Kingston competition on here and won a 2GB kit which looks to be great I can't wait until it arrives.
Anyway get OCZ you will be very unlucky if your not pleased to death with them, I have had 4 sets of OCZ and all of them have overclocked superbly.