There's no hard and fast rule if you want 1066 Mhz DDR speeds. Decent modules rated at that speed will run at the prescribed latency settings and well within or below the voltage spec for the particular module and kit.
Some DDR2-800s are terrific over-clockers and you can probably get them to 1000 or 1066 by loosening the stock latency timings and/or increasing the voltage.
I've been a Crucial Tracer/Ballistix fan until last year, when many complained of short longevity even within the maximum voltage. My third Crucial kit went south about two weeks ago -- DDR2-800s -- and run at 2.10V and 4,4,4,12, 2T @ DDR=835.
Since then, I've discovered two or three models of G.SKILLs that are great in various flavors: DDR2-1000, DDR2-800 and DDR2-900. The 900's are on their way from the Egg as I speak, and will run at DDR=900 Mhz with 4,4,4,12 timing which are the stock spec. People report that they run reliably at those settings with a voltage just below the minimum in the spec voltage range.
I run the 1000's at DDR=800 with tighter timings. I'm looking to overclock my Wolfdale system a couple hundred Mhz higher than it already is, 1:1 with the RAM, with prospect of pushing the memory toward 900 and those latencies.
Another brand I've discovered -- probably mentioned above -- is Corsair DHX. I got a DDR2-800 4GB 2x2 kit, and they are reliable at their spec and over-clockable. From my experience with the Crucials, I am nevertheless watchful about voltage settings. The Corsair only specifies a "recommended" voltage, but I got it from their support people that they honor the warranty for a 5% variance above that voltage. That is, you can push the 2.1V recommended setting to 2.2 and feel safe under the warranty. Even so, many benchtest reviews show that these can be volted to 2.4V for dramatic over-clocking.
The G.SKILLs that I have on order come in DDR2-800 and the DDR2-900 flavor for a price posted a couple days ago at the Egg of about $50. The DDR2-1000's have a much higher price tag. These are the "PI - Black" modules with what appears to be a heatspreader technology/design similar to the Corsair DHX kits. The $50 bargains are also PI-Black models in 4GB kits of 2x2.