The reference clock is the base frequency from which the DRAM speed is calculated from. A 2:8 ratio implies a 533.6MHz DRAM speed, or 1067.2MHz effective.
The modules are quite flexible in their timings and speeds, according to the SPD information. Loosen them up a bit, to 9-9-9-27 say, and DDR3-1,333MHz shouldn't be a reach.
And here's a Qimonda pack, which is practically identical save for the lower capacity - 3GB vs. 6GB.