4-7% boost in what? Games and most apps will run exactly the same at CL5 or CL4 timings.well 4-4-4-12 gives u about 4-7% profomance boost than 5-5-5-15 but 4G at 5-5-5-15 would be better
than 2G at 4-4-4-12 anyway if u want 4-4-4-15 just get a couple of heat spreaders an put them on an then lower the timings of your 5-5-5-15 to 4-4-4-12 thats what i did