This is an older article (2006)...still looking...
"Depending on CPU clock frequency, tight timings have a performance advantage over relaxed timings in CPU/memory intensive applications, ranging from 2% at 2 GHz to 6% at 2.6 GHz."
"When leaving the timings untouched at a CPU clock of 2 GHz or 2.6 GHz respectively, DDR600 performs 2% or 5% better than DDR400 in CPU/memory intensive applications."
http://www.tomshardware.com/reviews/tight-timings-high-clock-frequencies,1236.htmlFor $6 difference, I guess it's worth it for a hypothetical 2-5%. I guess I missed the memo when 1066mhz DDR2 wasn't $80 for 2gb. But the 2-5% performance gain would be in a application that requires maximum memory utilization. If it was a $40 difference, the money would be better vested in a faster CPU or better video card.
From that aside and from possibly giving Stogie a headache, go with the 1066.