I use elixir pc3500, but can only run at 400 speed with spd and "normal" on the timings. My msi 655 max board doesn't use numbers for timings, but "normal", "fast" etc. On a gigabyte board, I was able to run at 423 with this memory. Gigabyte set this board slightly overvolted, making it possible to run at the faster setting. I would try for 166 and 1:1 ratio, and you might have to bump up the memory voltage to 2.6 or 2.7. I also use the 2.4b, but mine won't run stable above 150, no matter how high I set the voltage. I would definately use case 2.5; elixir sometimes won't post with case 2. You won't notice the difference.