You don't know this and decided to OC?
That's quite dangerous...
1066MHz @ 5-5-5-18 would be slightly slower than 800MHz @ 4-4-4-12. Why? 1/1066 x 5 < 1/800 x 4
1/1200x5 = 0.0041s
1/1066x5 = 0.0047s
1/800x4 = 0.005s
DDR2-1200 MHz (5-5-5-15):
Int/Floating Bandwidth: 8114.67/8123.33
DDR2-800 MHz (4-4-4-12):
Int/Floating Bandwidth: 7156/7163.33
All testing done on Transcend AxeRam with a 1600 MT/s FSB.
Speed is everything, timings are secondary (imo).